. Analysis of development. Embryology; Embryology. 500 Special Vertebrate Organogenesis prospective conjunctival ectoderm in the ab- sence of contact with the optic vesicle re- mains pigmented and opaque like the sur- rounding true epidermis. The ectoderm thus appears to have a primordial capacity to form epidermis. Inasmuch as the mesoderm is a relatively thick layer, the upper surface of which is in contact with skin ectoderm while its lower surface is in close union with gut entoderm and is the source of a variety of organs and tissues, the question arises as to what portion of the mesoderm
. Analysis of development. Embryology; Embryology. 500 Special Vertebrate Organogenesis prospective conjunctival ectoderm in the ab- sence of contact with the optic vesicle re- mains pigmented and opaque like the sur- rounding true epidermis. The ectoderm thus appears to have a primordial capacity to form epidermis. Inasmuch as the mesoderm is a relatively thick layer, the upper surface of which is in contact with skin ectoderm while its lower surface is in close union with gut entoderm and is the source of a variety of organs and tissues, the question arises as to what portion of the mesoderm contributes to the formation of the dermis. Does the (the unsegmented mesoderm lateral to the somites, within which the body cavity arises) plus the closely united ectoderm and ento- derm will also produce normal skin and skin derivatives (feathers or hair, as the case may be) when grafted to the embryonic chick coelom as seen in Figure 192 (Rawles, '47; Straus and Rawles, '53) or to the chorio- allantoic membrane (Murray, '28). In view of the fact that it is assumed fre- quently on the basis of morphological studies (Engert, '00, and others) that the dermis, not only of the dorsal and dorsolateral re- gions but of the other body regions as well, P. Fig. 192. Section through skin and do^^^^ feathers developing in intracoelomic graft of lateral plate isolated from right side of 28-somite chick embryo at level of somites 22-25. Total age 10^/^ days. Compare with skin and feather germs of normal. Fig. 193 C. Iron hematoxylin, Sfi X 75. dermis arise directly from mesodermal cells which are everywhere in contact with and subjacent to the skin ectoderm, or is its origin restricted to the so-called "derma- tome," one of the three arbitrary divisions of the somite? An imequivocal answer to this old and controversial problem has been fur- nished for the chick and the mouse by the use of experimental techniques. Isolates of early limb buds, taken prior to the entrance of cells
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
