THE ANATOMICAL RECORD 218:88-93 (1987) Taste Bud Development in Chickens (Gallus gallus domesticus) JUDITH R. GANCHROW AND DONALD GANCHROW Department of Oral Biology, The Hebrew University-Hadassah School of Dental Medicine, Jerusalem 91010 (J.R. G.), and Department ofAnatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Tel-Aviv 69978 (D.G.), Israel ABSTRACT Oral epithelium in the anterior mandibular glands region was examined in embryonic, hatchling, and mature chickens to establish the timing of morphologic events during taste bud ontogeny. Hematoxylin-and-eosin-stainedsections (10 pm) from 27 Anak (broiler breed) chickens were examined serially, and buds were quantified at 16-20 days of incubation (E) and, posthatch days 1 and 5060. Taste buds were first recognized at the beginning of E17 as small clusters of cells in the basal epithelium. Only spherical-shapedbuds were observed on E17 and E18, and these spherical clusters never penetrated to the surface of the stratified epithelial layer. E19 marked a transitional stage when mature bud features began to emerge: the buds assumed a more elongate shape, several kinds of cells comprising the bud were distinguishable and the first taste pores were observed. During the ensuing embryonic days, buds continued to elongate commensurate with the deepening oral epithelium and by hatching virtually all buds opened to the oral cavity. No marked morphological changes in taste bud structure were observed on the day of hatching and at 50-60 days posthatching. Taste bud numbers increased dramatically during E17 and E18, peaked on E19, and remained relatively constant thereafter. It is concluded that the morphological sequence of taste bud development in chickens is similar to that in mammals. The timing of bud ontogeny, though initiated only during the third trimester in ovo, essentially is completed by hatching, thus providing the precocial hatchling with the sensory apparatus essential for gustatory experience. The sequence of events in the development of taste buds is relatively consistent across mammalian species (cf. Bradley, 1972; Bradley and Mistretta, 1973; Bradley and Stern, 1967; Bradley et al., 1980; Farbman, 1965; Ferrell, 1984; Komatsu and Yamasaki, 1980; Stedman et al., 1983; Zahm and Munger, 1983a,b).Initially, presumptive buds are recognized as small clusters of cells in the basal epithelium. Early developing taste buds are covered by superficial layers of epithelium, thereby remaining isolated from the environment of the oral cavity. Later in development the buds elongate as their cells become oriented perpendicular to the basement membrane epithelium. Bud maturity is usually defined when a pore is formed as a channel communicating between the apices of the taste bud cells and the oral cavity. Marked increases in the number of taste buds also occur during these progressive stages. To what extent this morphogenetic sequencing during mammalian bud ontogeny is generally applicable to that in other vertebrates is not known. For example, the evolution of avian and mammalian forms from different reptilian ancestors (Romer, 1941) argues for elaborating and comparing the developmental bud sequence in these vertebrate species. Unlike the uniform sequencing of events in bud development, the time of appearance of the first buds in mammals varies with time in utero. Ferrell (1984) suggested that the longer the gestational period, the earlier 0 1987 ALAN R. LISS, INC. in fetal life the taste receptors begin to develop. Thus, for humans (280 days gestation) and macaque monkeys (168 days gestation), taste buds begin to develop by the end of the first trimester (Bradley, 1972; Bradley and Stern, 1967; Zahm and Munger, 1983a); in sheep (147 days gestation) bud development is initiated early in the second trimester (Bradley and Mistretta, 1973);for puppies (Ferrell, 1984) and kittens (Stedman et al., 1983) (62-63 days gestation) bud development commences near the middle of the third trimester; the first signs of immature buds in rats (21 days gestation) and rabbits (30 days gestation) appear only at the end of the third trimester (Hermann, 1884; Lustig, 1884; Mistretta, 1972). The data above might imply that bud development in chicks (21 days in OVO) should originate close to the time of hatching. However, though rats and chicks have the same length of gestation, their maturational state at birth and hatching differs. Rats are altricial mammals, and isolated, mature taste buds are not apparent until several days after birth followed by a great increase in numbers of buds during the suckling period (Mistretta, 1972). In contrast, newly hatched chicks are precocial avians and hatchlings already possess a considerable array of mature buds located in the oral epithelium of Received July 7, 1986; accepted October 22,1986. 89 CHICKEN TASTE BUD DEVELOPMENT the upper beak (palate), anterior mandibular glands region of the lower beak, posteroventrolateral region of the anterior tongue, and oral epithelium posterior to the lingual spines (Ganchrow and Ganchrow, 1985; Saito, 1966). Taste discrimination tests show that these buds are indeed functional at hatching (Braun-Bartena et al., 1986) as well as during the last embryonic day Wince, 1977). These data suggest that the onset of taste bud development might be initiated well before hatching within the relatively short gestational period. The present study provides quantitative and descriptive light microscopic data on the morphogenetic sequence and timing of anterior mandibular taste bud development in the domestic chicken. Anterior mandibular buds are concentrated in the sublingual region of the lower beak oral epithelium. Their viability is dependent upon the integrity of the chorda tympani branch of the facial nerve (Ganchrow et al., 1986b), which transmits primary afferent gustatory information from these buds to somata of the geniculate ganglion (Gentle, 1983, 1984; personal communication), and further centrally, to subnuclei related to the solitary tract in the brainstem (Ganchrow et al., 1986a; Gentle, 1979). animal. Several transitional morphologic stages occur in the developing taste bud, and these stages are clearly differentiable from the epithelial surround by the organization and staining characteristics of the bud. However, during quantification of taste buds, morphological differences were disregarded. Each bud was traced serially through its entire extent and counted only once. Occasionally the base of one bud appeared to be continuous with the base of an adjacent one; these were counted as two separate buds since they approached the superficial epithelial layers independently. Number of gland duct openings was also noted. Results are expressed as averages plus or minus the standard error of the mean unless stated otherwise. RESULTS Quantitative Considerations Gustatory receptor development in the chicken is characterized by a rapid establishment of the bud population during the last trimester before hatching, which is substantially maintained over the ensuing 8 posthatching weeks. In the region of the anterior mandibular glands, no clear taste bud primordia were observed until after the onset of the 16th embryonic day (E16). MATERIALS AND METHODS By the beginning of E17, the initial sign of taste buds Observations were made on 27 Anak strain (broiler (mean = 16 f 4) appeared. Numbers of buds increased breed) chickens supplied by the Kibbutz Tzuba Hatchery through E18 (mean = 36 f 8) and E19 (mean = 83 f 2) (Jerusalem). Either eggs prior to incubation (i.e., “day and ranged between 60 and 80 over the remaining ages 0”) or 1-day-old hatchlings were obtained. Eggs were examined (E20, 72 _+ 6; H1, 61 _+ 8; and H50-60, 57 _+ incubated at 99.6”F, saturated humidity, in a rotating, 8). In the lower beak epithelium sampled, taste buds only forced-draft incubator (Modern Equipment, Inc., Haifa), while hatchlings were either utilized immediately or appeared adjacent to ducts of the anterior mandibular maintained in the Hebrew University-Hadassah Medi- glands that opened into the floor of the mouth. However, cal School Animal Facility. Light and electron micro- gland duct openings did not necessitate the presence of scopic sampling of supplementary lower beak oral tissue a taste bud, especially in the lateral edge of oral epitheprior to this report established that there were no clear lium or posteriormost regions adjacent to the lingual signs of buds throughout the first 15 days of incubation. frenulum. Mandibular salivary glands in the chicken Toe and beak lengths also were measured to define the begin to develop on E8 as a series of solid ingrowths of embryonic stage in the last trimester of development the mucosa, and by E16 the population of gland ducts (Hamburger and Hamilton, 1951).While third toe length that open to the oral surface is well established (Hamilcompared favorably with the atlas developmental stages, ton, 1952; and personal observations).The average numupper beak length in our breed was at variance. Hence ber of anterior mandibular gland duct openings was in our material, number of incubation days (E) was 27 f 1 in the anteroposterior extent of the bud region considered preferable to staging as the embryonic index sampled across all the ages. The variation in the numbers of gland duct openings and taste buds correlated of age. The dissected beaks from 17 younger embryos (E16- positively (r = 0.74, P < .Ol) after the bud population 19) were immersion-fixed in 10% neutral buffered for- count had peaked (i.e., at E19 and older). When taste malin. The remaining ten older animals-three at E20, buds were initially forming at E17-18, the bud-gland three hatchlings (Hl), and four 50-60-day-old (H50-60) duct opening correlation approached significance (r = chickens-were anesthetized with 6% pentobarbital so- 0.67; P = .05). Thus individual variability in the numdium (Hadassah), the blood was flushed transcardially ber of gland duct openings may partially account for the with heparinized saline, and the chickens were perfused variability in the total number of buds observed. A more transcardially with 10%neutral buffered formalin. Then accurate representation of taste bud development is the lower beak was immediately placed in 10% neutral therefore a ratio of buds-to-glandduct openings. Figure buffered formalin where it remained for at least a week. 1 shows that the number of taste buds per gland duct Oral tissue extending from the beak tip to the lingual opening increased exponentially during the first portion frenulum was dissected free and postfixed in the same of the last embryonic trimester (E16-18) and reached a solution for several additional days. Subsequently, the plateau of about 2.5 buds per opening in the ensuing tissue was decalcified (Rapid Bone Decalcifier, Du-Page prehatching (E19 and E20) and posthatching (H1 and Kinetic Laboratories), dehydrated in increasing concen- H50-60) periods. This developmental index seems relitrations of ethanol, and embedded in paraffin. Frontal able since, independently, Kusuhara (personal commusections (10 pm) were stained with hematoxylin-and- nication) analyzed anterior mandibular buds in seven mature chickens and obtained a similar ratio of 2.23 eosin for light microscopic examination. Analyses of taste bud morphology, number, and den- budslgland duct opening. Since the lower beak continued to grow throughout sity were made unilaterally in each processed block of bilateral tissue without foreknowledge of the age of the the ages examined, the density of buds decreased mark- 90 J.R. GANCHROW AND D. GANCHROW i I (31 E16 . E17 7.c E18 E19 AGE E20 H1 - H 50-60 (DAYS) Fig. 1 . Mean (+SE.) number of taste buds per anterior mandibular glands duct (AMQ opening as a function of embryonic age (E16-E20) and posthatching(Hl-H60) age. The number of cases sampled at each age appears in parentheses. edly once the total population had been established. For example, at E20, the bud region (2.83 k 0.07 mm anteroposterior extent) contained 25 f 1 buds/mm. At hatching, this density had decreased to 19 +_ 3 budslmm over a distance of 3.16 f 0.14 mm, and by H50-60, 9 +_ 1 budslmm were distributed over 6.66 +_ 0.46 mm. The region of the lower beak oral epithelium containing taste buds generally constituted about the middle 75% of the length of tissue examined. Morphologic Considerations Figure 2A illustrates oral epithelium and a gland duct (*) at E16, the oldest age at which buds still were not apparent. The epithelium consists of a single basal cell layer covered by two to three strata of flattened cells. The cuboidal cells lining the gland duct still extend somewhat beyond the duct opening borders. Based on previous data (Ganchrow and Ganchrow, 1985), at the point where epithelium meets glandular tissue, one might expect to find a taste bud. There are a few lighter staining cells (curved arrows), which may represent the taste bud Anlage in this region. Only two instances of such possible precursor cells were observed at E16 within the otherwise uniform oral epithelium. Immature taste buds initially were identified at E17. The course of bud maturation may be divided into two main time frames based on bud shape: the spherical and ovoid stages. The percentages of buds perceived to be in the spherical stage were 94% at E17, 85% at E18, 32% at E19, 13%at E20, and none thereafter. Figure 2B-D illustrates three types of spherical-stage buds characteristic of ages E17, E18, and E19. Spheres varied in their size and depth within oral epithelium. The earliest identified buds were spherical clusters of cells located in the deepest epithelial layers (Fig. 2B,C). Some bud cells appeared slender and elongated already at E17, although their axial orientation could vary (Fig. 2B,C). The cytoplasm of some bud cells stained slightly less intensely, and fewer still stained more intensely, than that of the epithelial surround. Bud cell nuclei were somewhat larger and as intensely stained as those in basal epithelium. In some locations, the epithelium at this stage had differentiated to include a third, intermediate layer whose cells contained more cytoplasm and smaller, paler-staining round nuclei than those in adjacent basal and superficial layers. The surface layer of flattened stratified epithelial cells was three to four cells in height and sometimes appeared desquamate. By E18, the basalmost deeper-staining layer had expanded to about three cells deep, and the superficial stratified layer was about eight to nine cells thick. Fine tubules penetrating the developing bud were already apparent at this spherical bud stage (thick arrows Fig. 2C, D). Widediameter buds (Fig. 2D) multiply insinuated with fine tubules were mainly noted at E18 and E19. Embryonic day 19 represented the second transitional phase in bud maturation. The spherical structures began to elongate to an ovoid shape that extended the entire thickness of the oral epithelium, such that the long axis of the bud was oriented perpendicular to the basal and surface epithelial layers. Once the surface epithelium was invaded by the bud, a taste pore became apparent (fine arrow, Fig. 2E); occasionally, multiple pores were observed (cf. in mammals: Bradley, 1972; Ferrell, 1984; Heidenhain, 1914; Zahm and Munger, 1983b). At this stage, fine tubules still were a consistent feature in the bud (thick arrow, Fig. 2E), and lighterstaining cells were more easily seen at the bud apex than on earlier embryonic days. As more buds elongated to the ovoid stage, characteristics of mature taste buds were expressed further (cf. Figs. 2F, H1 and 2G, H50-60). The basal half of the bud clearly contained lighter-staining cells with large, round, medium-staining nuclei interspersed among darker cells with lighter-staining nuclei. The basal half of the buds was ensheathed by small cells with darker-staining nuclei. The pore region was flanked by long, narrow apical bud cells oriented approximately perpendicular to the epithelial surface in an orderly arrangement around the pore (Figs. 2E and F). These slender cells contained slim, dark-staining as well as lighter-staining round nuclei located distal to the pore. Adult buds retained these main features (Fig. 2G). Neither pore opening nor other morphologic signs of communication between the bud and oral cavity were observed prior to E19. In contrast, from E19 and later, three modes of pore opening were seen. The usual mature pore form was a narrow (1-2 pm), shallow channel whose walls are composed of superficial epithelial cells (Fig. 2E,F). Sometimes this channel appeared in a widened form (Fig. 2G) more closely resembling a pit (Fig. 2H). Rarely, the taste pore and the fine tubules of the bud seemed to be continuous, as if a single channel had penetrated through to the basal bud regions. Figure 21 is a montage of a bud from two adjacent sections, showing one such long channel directed toward a tubule in the bud base. Since the tubule is cut in cross-section,it appears as the hollow center of a cellular rosette. This rosette-like configuration is a usual feature in mature CHICKEN TASTE BUD DEVELOPMENT Fig. 2. Events in taste bud development. Asterisks in all photographs indicate gland duct openings or the location at which the duct will open in an adjacent section. A Oral epithelium 1 day prior (E16) to the spheroidal stage of bud development. The curved arrows indicate a collection of four cells (identified in several planes of focus) located at the junction of glandular and epithelia1 cells. This configuration may represent the taste bud primordium (10pm X 10 pm). E16. Magnification, x400. B: A small, spheroidal, presumptive bud (18 pm x 20 pm) (curved arrow) in the basal oral epithelium. E17. Magnification, X 160. C: Spherical bud (50 pm x 40 pm) with tubule (arrow). E17. Magnification, x 160. D: Large spherical bud (76 pm x 76 pm) with multiple tubules seen in cross-section. Arrow points to one such tubule. E19. Magnification, x200. E: Ovoid taste bud (width: 50 pm) with a pore opening. Fine arrow indicates pore (2 pm). Note orientation of apical 91 bud cells toward the pore. Thick arrow points to tubule in cross-section. E19. Magnification, x 160. F: Two taste buds (widths 50 pm, left; 35 pm, right) surrounding a salivary gland duct opening. Pores are marked with arrows. Note the orientation of apical bud cells toward the pore (widths, 1-2 pm). H1. Magnification, x 160. G: Mature taste bud with pore (fine arrow). Pore width = 25 pm. Note the orientation of apical bud cells toward the pore and ductule (thick arrow) cut in cross-section. H50-60. Magnification, x 100.H: A taste pit opening (fine arrow). Pit width = 21 pm. Thick arrow points to tubule in cross-section. H1. Magnification, ~ 2 0 0 I:. Montage of two adjacent sections showing a bud tubule directed toward a taste pore (fine arrow). The lowest portion of the tubule is indicated by the thick arrow. E20. Magnification, x200. 92 J.R. GANCHROW AND D. GANCHROW TABLE 1. Variability in the number of anterior mandibular taste buds in the posthatch chicken: Light microscopic, serial section analyses Age H1 H1 H1 H56 H60-70 Strain Mean Range Reference Anak (broiler) White leghorn Yarkon-tinted Brown leghorn Anak (broiler) 122l 84 49 56 114l 88-158l 54-103 27-63 44-74 92-136l Present study Saito (1966) Ganchrow and Ganchrow (1985) Gentle and Hunter (1983) Present study ‘Unilateral bud counts were doubled to derive an estimate of buds in the entire anterior mandibular bud region. taste buds (Berkhoudt, 1985; Ganchrow and Ganchrow, generating elements. Moreover, perhaps by chance the 1985; Ganchrow et al., 198613; Gentle, 1971; Kurosawa sample of E19 chick embryos utilized was biased toward animals with more salivary duct openings in the anteet al., 1983; Saito, 1966). rior mandibular bud region than the sample of animals DISCUSSION at the other ages. Since a significant correlation beWithin the last trimester of a relatively short gesta- tween the number of buds and duct openings was obtion period (21 days), chick embryos display a rapid served in the present study, the latter variable could development of taste buds. Specifically, anterior man- parsimoniously account for the large number of buds dibular taste bud development begins around E17, pro- observed at E19. Intra- and interstrain variability exists in the numceeds through a morphological sequence of events similar to that described for mammals, and by H1 the full bers of chicken taste buds. Table 1summarizes the light population of buds with mature features has been estab- microscopic bud counts in the anterior mandibular lished. Thus, unlike the delayed onset of bud develop- glands region in different strains of posthatch chickens. ment observed in altricial mammals with similarly Clearly, the ranges in bud numbers and the means are short, gestational periods (rats: Mistretta, 1972;rabbits: quite variable. The method of bud counting could acLustig, 1884; Hermann, 1884), chicken taste buds de- count for some of this variability, but even in the same velop sufficiently early in the embryo to provide a taste laboratory and using the same observers and counting receptor population commensurate with the hatchling’s methods, 1-day-oldbroilers (Anak strain) displayed more precocial maturational state. Active ingestion of am- than twice as many buds as lighter-weight chicks bred niotic fluids commences during the week preceding the for egg laying (Yarkon-tinted). Assuming that higher onset of taste bud development, and thus, the forming anterior mandibular bud counts in the Anak strain rebuds are potentially stimulated by the increasingly con- flect a greater density of taste buds throughout the oral centrated egg fluids during the final embryonic week cavity and that the number of buds is related to taste (Romanoff, 1960). sensitivity, these results would be compatible with reBud counts in the chick increased rapidly compared to cent data showing that heavier-breed chickens have a most mammalian species, such that within 3 days bud greater overall taste sensitivity than do lighter breeds numbers reached a unilateral total of 83 f 2 buds. This (Barbato et al., 1982). total at E19 was somewhat high compared to all other ACKNOWLEDGMENTS ages analyzed suggesting an embryonic “overshoot” in This research was supported by a grant from the the pool of gustatory receptors produced prior to bud maturation, with subsequent bud degeneration until a United States-Israel Binational Science Foundation stable taste bud population evolved. Cell death in the (BSF), Jerusalem, Israel. A preliminary report of these developing nervous system is a well documented phe- findings was presented at the IX International Symponomenon (e.g., Barnett, 1985; Rubel et al., 1976). In the sium on Olfaction and Taste, Snowmass, Colorado, July striped dolphin, the entire perinatal taste bud popula- 1986. We would like to thank Ilana Frank and Dr. Ron tion disappears before adulthood (Komatsu and Yama- Goldstein for their technical assistance, Eva Salomon saki, 1980),which represents a kind of phylogenetic cell for her photographic expertise, Shula Konig for typing death. If the pattern of bud innervation in embryonic the manuscript, and Kibbutz Tzuba for supplying the chickens is similar to that in adult mammals with sev- eggs. LITERATURE CITED eral nerve fibers innervating an individual bud (e.g., Beidler, 1969; Miller, 1971), and since the integrity of Barbato, G.F., P.B. Siegel, and J.A. Cherry (1982) Genetic analyses of gustation in the fowl. Physiol. Behav., 29:29-33. avian taste buds requires an intact nerve supply (GanR.I. (1985)Developmental neuron cell death in dystrophic and chrow et al., 1986b; Gentle, 19711, such a bud cell death Barnett, normal chickens. Exp. Neurol., 89:382-390. event would require an unusually selective degenera- Beidler, L.M. (1969)Innervation of rat fungiform papilla. In: Olfaction tion or a restricted branching pattern of primary afferand Taste 111. C. Pfaffmann, ed. The Rockefeller University Press, New York, pp. 352-369. ents in the chick embryo. Jacobson (1978) argued that H. (1975) Special sense organs: Structure and function of nervous system cell death is not ubiquitous but occurs Berkhoudt, avian taste receptors. In: Form and Function in Birds. AS. King primarily where a 1:1 neuron-target cell relationship and J. McLelland, eds. Academic Press, New York, Vol. 3, pp. 463exists. Frankly degenerating taste buds were not ob496. served on E20 and H1 although very rapid cell degener- Bradley, R.M. (1972) Development of the taste bud and gustatory papillae in human fetuses. In: Third Symposium on Oral Sensation ation and removal of debris cannot be discounted; and Perception: The Mouth of the Infant. J.F. Bosma, ed. Charles hematoxylin-and-eosin staining of our embryonic oral C. Thomas, Springfield, IL, pp. 137-162. material also may have obviated our observation of de- Bradley, R.M., M.L. Cheal, and Y.H. Kim (1980)Quantitative analysis CHICKEN TASTE BUD DEVELOPMENT of developing epiglottal taste buds in sheep. J. Anat., 130;25-32. Bradley, R.M., and I.B. Stern (1967)The development of the human taste bud during the foetal period. J. Anat., 101:743-752. Bradley, R.M., and C.M. Mistretta (1973)Gustatory senses in foetal sheep during the last third of gestation. J. Physiol. (Lond.), 231:271282. Braun-Bartena, A., J.R. Ganchrow, and J.E. Steiner (1986)Behavioral reactions to taste stimuli in hatchling chicks. Ann. N.Y. Acad. Sci., in press. Farbman, A.I. (1965)Electron microscope study of developing taste buds in rat fungiform papilla. Dev. Biol., 11:llO-135. Ferrell, F. (1984)Taste bud morphology in the fetal and neonatal dog. Neurosci. Biobehav. Rev., 8:175-183. Ganchrow, D., and J.R. Ganchrow (1985)Number and distribution of taste buds in the oral cavity of hatchling chicks. Physiol. Behav., 34:889-894. Ganchrow, D., J.R. Ganchrow, and M.J. Gentle (1986a)Central afferent connections and origin of efferent projections of the facial nerve in the chicken (Gallus gallus domesticus). J. Comp. Neurol., 248:455-463. Ganchrow, J.R., D. Ganchrow, and M. Oppenheimer (1986b)Chorda tympani innervation of anterior mandibular taste buds in the chicken (Gallus gallus domesticus). Anat. Rec., 216:434-439. Gentle, M.J. (1971)The lingual taste buds of Gallus domesticus L. Br. Poult. Sci., 12:245-248. Gentle, M.J. (1979)Single unit responses from the solitary complex following oral stimulation in the chicken. J. Comp. Physiol. 130:259-264. Gentle, M.J. (1983)The chorda tympani nerve and taste in the chicken. Experientia, 39:1002-1003. Gentle, M.J. (1984)Sensory functions of the chorda tympani nerve in the chicken. Experientia, 40:1253-1254. Gentle, M.J., and L.N. Hunter (1983)The anterior mandibular taste buds in the chicken. IRCS Med. Sci., 11:845. Hamburger, V., and H. Hamilton (1951)A series of normal stages in the development of the chick embryo. J. Morphol., 88:49-92. Hamilton, H.L. (1952)Lillie’s Development of the Chick: An Introduction to Embryology,,Henry Holt & Co., New York, pp. 377-378. Heidenhain, M. (1914)Uber die Sinnesfelder und die Geschmacksknospsen der papilla foliata des Kaninchens. Arch. Mikrosk. Anat., 85:365-560. Hermann, F. (1884) Beitrag zur Entwicklungsgeschichte des Ge- 93 schmacksorgans beim Kaninchen. Arch. Mikrosk. Anat. 24:216229. Jacobson, M. (1978)Developmental Neurobiology. Plenum Press, New York, p. 284. Komatsu, S., and F. Yamasaki (1980)Formation of the pits with taste buds at the lingual root in the striped dolphin, Stenella coeruleoalba. J. Morphol., 164:107-119. Kurosawa, T., S. Niimura, S. Kusuhara, and K. Ishida (1983)Morphological studies of taste buds in chickens. Jpn. J. Zootech. Sci., 54.502-510. Lustig, A. (1884)Beitrage zur Kenntniss der Entwickelung der Geschmacksknospen. Sitzungsberichte Kaiser Akad. Wiss. Wien Mathematische-NaturwissenhaftlicheClasse, 89:308-324 (Abtl. 3). Miller, I.J. (1971)Peripheral interactions among single papilla inputs to gustatory nerve fibers. J. Gen. Physiol., 57:l-25. Mistretta, C.M. (1972)Topographical and histological study of the developing rat tongue, palate, and taste buds. In: Third Symposium on Oral Sensation and Perception: The Mouth of the Infant. J.F. Bosma, ed. Charles C. Thomas, Springfield, IL.pp. 163-187. Romanoff, A.L. (1960)The Avian Embryo. Structural and Functional Development. The Macmillan Co., New York, pp. 1110-1111. Romer, A.S. (1941)Man and the Vertebrates. University of Chicago Press, Chicago. Rubel, E.W., D.J. Smith, and L.C. Miller (1976)Organization and development of the brain stem auditory nuclei of the chicken: Ontogeny of n. magnocellularis and n. laminaris. J. Comp. Neurol., 166:469-490. Saito, I. (1966)Comparative anatomical studies of the oral organs of the poultry. V. Structures and distribution of taste buds of the fowl (in Japanese). Bull. Fac. Agric., Miyazahi University, 13:95-102. Stedman, H.M., C.M. Mistretta, and R.M. Bradley (1983)A quantitative study of cat epiglottal taste buds during development. J. Anat., 136:821-827. Vince, M.A. (1977)Taste sensitivity in the embryo of the domestic fowl. Anim. Behav., 25:797-805. Zahm, D.S., and B.L. Munger (1983a)Fetal development of primate chemosensory corpuscles. I. Synaptic relationships in late gestation. J. Comp. Neurol., 213:146-162. Zahm, D.S.,and B.L. Munger (1983b)Fetal development of primate chemosensory corpuscles. II. Synaptic relationships in early gestation. J. Comp. Neurol., 219:36-50.