On the relations between the mesenchy-mal spaces and the development of the posterior lymph hearts of turtles.код для вставкиСкачать
ON THE RELATIONS BETWEEN THE MESENCHYMAL SPACES AND THE DEVELOPMENT OF T H E . POSTERIOR LYMPH HEARTS O F TURTLES FRANK A. STROMSTEN From the Laboratories of Animal Biology, State University of Iowa THREE FIQURES In a recent paper read before the American Society of Zoologists, Central Section, the writer called attention to the fact that, in the turtles, the mesenchymal spaces play a much more important part in the development of the lymphatic system than they seem to play in mammals. In a later paper before the Iowa Academy of Science, on the “Development of the Posterior Lymph Hearts of the Loggerhead Turtle,” considerable stress was placed upon the importance of the intercellular lymph spaces in initiating the development of the lymph hearts. Since then a more careful study has been carried on with special reference t o these spacesin embryos just before, at the time of, and immediately after the first appearance of the anlagen of the posterior lymph hearts. It is the purpose of this paper to consider merely a few of the results obtained by this study. A more detailed account is reserved for a later paper on the anatomy and development of the entire lymphatic system of the loggerhead turtle. The embryonic material forming the basis for this work was collected by the writer at the Marine Laboratory of the Carnegie Institution at the Dry Tortugas, Florida. I wish here to express my deep obligations to Dr. Alfred G. Mayer, Director of the Torh g a s Station, for valuable assistance in collecting the material ; and to Professor Gilbert L. Houser for many helpful suggestions during the pursuance of this investigation. I78 174 FRANK A. STROMSTEN A great deal of attention has’been paid to the methods of preparing the materials for study during this research. It is extremely important for the correct interpretation of the significance of the mesenchymal spaces that the tissues of the embryo should be preserved in as nearly their natural condition as possible. A full account of the methods Will be given in the later paper. The posterior lymph hearts of turtles are a pair of elliptical, pulsating organs situated immediately below the carapace, just back of the upper ends of the iliac bones, one on each side of the body. They drain the lymph cavities and lymph channels of the posterior extremities and pelvic regions, and open into tributaries of the posterior renal advehent veins. The only important work that has hitherto been done in the development of the sauropsidian lymph hearts, as far as is known t o the writer, is that on the chick by Sala (’00). According t o Sala’s researches, the posterior lymph hearts are derived from the first five coccygeal veins of each side by a process of dilation and confluence. He finds that small spaces or fissures develop in direct connection with the lateral branches of these veins. These fissures appear to be merely the simple dilation and ramifications of the veins themselves. These spaces or fissures enlarge and fuse with each other, producing a “system of cavities, very irregular in form and dimensions, intercommunicating, and connected at the same time with the lateral branches to the first five coccygeal veins.” The cavities subsequently fuse to form a single cavity for each lymph heart.’ The posterior lymph hearts of the turtles are closely related in their development to the formation of a pair of vessels, extending along the outer surface of the muscle plates of the post-iliac regions, and forming one of the main tributaries of the renal portal system of each side. This pair of veins we shall designate in this paper as the right and left caudal branches of the posterior renal advehent veins. They correspond to the venae ischiadicae of many authors. The right and left caudal branches of the renal advehent system 1 Sala; “ Sviluppo dei Cuori Linfatici e dei Dotti Toracici nell ’Embrionedi Pollo,” pages 269 and 270. See, also, Huntington; Anatomical Record, vol. 2, p. 34. POSTERIOR LYMPH HEARTS OF TURTLES 175 arise by the longitudinal anastomosis of the dorsolateral branches of the postcardinal veins, posterior to the opening of the iliac veins, and just outside of the muscle plates. They continue backward into the tail as the lateral coccygeal veins, and forward as the main branches of the advehent system of the Wolffian bodies. The development of the lymph hearts is directly related to that portion of these veins formed by the first two or three post-iliac branches of the postcardinal veins. The development of the posterior lymph hearts is initiated in the loggerhead turtle by the vacuolation of the subcutaneous mesenchymal tissue of the post-iliac regions. As early as the middle of the second week of development, a noticeable change in the mesenchymal cells of this region is clearly seen. The mesenchyme becomes very loose and spongy. Toward the close of the second week, the mesenchymal spaces enlarge and fuse with each other. There is thus formed a network of intercommunicating spaces which invest and communicate with invading capillaries from the first two or three post-iliac branches of the postcardinals. Fig. 1 is a camera lucida drawing of a small portion of this area under the homogenous immersion lens. The spongy appearance is not sufficiently brought out in this drawing,yet it shows to some extent the nature of the vacuolation, and the relations of the spaces to the blood capillaries. By the middle of the third week of development, the dorsolateral branches of the postcardinal veins have fused at their distal ends to form the caudal branches of therenal advehent system. The formation of this pair of veins produces profound changes in the post-iliac spongy area. Great spaces or channels appear. These spaces seem to be enormously dilated capillaries which intercommunicate with each other, and connect with the accompanying veins at one or two points. They contain red blood cells, and are indistinguishable from the veins of that region, except by their position. They correspond to the venolymphatics of birds and mammals. Hand in hand with the formation of the veno-lymphatic channels, there occurs a condensation of the mesenchyme in their immediate vicinity. The great accumulation of lymph in this POSTERIOR LYMPH HEARTS O F TURTLES 177 region has now found an outlet into the venous system through the veno-lymphatic channels. The mesenchymal spaces are then either absorbed by the veno-lymphatics, or their walls collapse so that the tissue becomes much more compact than it formerly was. Immediately surrounding the veno-lymphatics the condensation has gone so far as to form definite walls for these channels. The veno-lymphatic anlagen of the lymph hearts increase rapidly in size, during the third and fourth weeks. A process of absorption of the septa1 walls between the several anlagen takes place during the later part of the fourth week. Beginning at the anterior end and proceeding posteriorly, the several spaces fuse with each other so that near the beginning of the fifth week, single cavities are formed for eachlymph heart. In the meantime, muscle cells have wandered in from the adjacent, muscle plates, completing the essential steps in the formation of t'he lymph hearts. Fig. 2 is a representation of the veno-lymphatics of a twenty-five day old embryo of the loggerhead turtle. The veno-lymphatic channels still contain red blood cells. They are readily distinguished from the accompaning vein by their denser walls. Fig. 3 is a section through the lymph heart of a loggerhead turtle embryo of thirty-two days development. The results of this investigation show that the mesenchymal spaces have an important function to perform in initiating the development of the posterior lymph hearts. The importance of the intercellular spaces is probably more clearly brought out in turtles than in birds and mammals, because in the latter we are dealing with more or less rudimentary structures. A study of the development of the anterior lymph sacs of the turtle, itself, would indicate as much. This, however, will be considered at another time. In the highly specialized, or, in some cases, rudimentary lymphatic structures of birds and mammals, the earlier stages are passed through too rapidly, and aqe too slurred or masked to enable one to determine accurately the exact condition of affairs. Even in the present series of turtle embryos, which represent stages preserved at morning, noon, and night for every day of development from the time of laying until hatching, it will 178 FRANK A. STROMSTEN be necessary during the present summer to fill in certain critical stages in order t o determine positively whether the veno-lymphatics represent true modified capillaries or not. There are indications that in the development of both the lymph hearts andthe lymph sacs of the loggerhead turtle, the mesenchymal spaces play an even more important part than has been assigned to them in this paper.