Volume 2

Text-book of embryology / edited by Walter Heape.

Date:
1914-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Text-book of embryology / edited by Walter Heape. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    68/616 (page 52)
    ect. As regards the Birds, which of the higher Amniotes alone concern us in this volume, there is com- plete agreement that they are to he looked on as highly-special- ized descendants oi' Reptilian ancestors. It follows therefore that their develop- mental phenomena should be considered in relation to the cor- responding pheno- mena in Reptiles. Leaving out of account certain vague phenomena which have been inter- preted, in the present writer's opinion un- justifiably, as remin- iscences of gastrula- tion processes (see Chapter X.), the for- mation of a gastrular lip seems to have Fig. 32. — Transverse sec- tions through region of nenrenteric canal of Che- Ionia embryo with about 16 segments. (jVfter Mitsnkuri, 1896.) The mid-clorsal ectoderm has become covered in to form the neural tube (s.c) as will be de- scribed in Chap. II. Fig- C shows the nenrenteric canal opening u)nvards through this, while Figs. H, D and E, taken from sections anterior and l)os-- terior t<i the neurent<^ric open- ing, show the continuity of tissue from (-ctodenn to endo- derm which is a characteristic feature of a primitive streak, pcf, ectoderm: <■<?, endoderm; raes, mesoderm; iV, notochord; iw.c, nenrenteric canal: s.c, spinal cord.