320 



THE CAT. 



[CHAP. x. 



membranes coexist is the germ area, or gastrodisc. In the central 

 portion of this, a third membrane soon makes its appearance (Fig. 



144). This is the mesollast, 

 and is thought to be derived 

 from the hypoblast,* by sub- 

 divisions of the cells of the 

 letter. The three-layered part 

 of the gastrodisc is a much 

 thickened part of it, and is 

 called the embryonal area, for it 

 is here that the embryo arises. 

 Up to this point the matter 

 which is eventually to become 

 the body of a cat shows no re- 

 semblance to any animal what- 

 ever. It is but an aggregation 

 of cells of protoplasm arranged 

 as just described, and is rather 

 comparable with some very 

 lowly organised fungus-like plant 

 than with anything we ordi- 

 narily understand as an animal. 

 5. It is in the midst of the embryonal area that the first sign 

 of the cat which is to be, is made manifest by the FIRST APPEARANCE 



Fig. 142. LONGITUDINAL SECTION THROUGH THE 



AXIS OF THE OVUM, IN WHICH THE EPIBLASTLC 



CELLS (e) HAVE ALMOST SURROUNDED THE 

 HYPOBLASTIC ONES (i). 



d. Central cell. 



o. ^Hypoblastic cell, occupying the interspace 

 left at one point by the epiblas 



astic cells. 



A. Commencing separation between th 

 blastic and hypoblastic cells. 

 e. Epiblast. 

 i. Hypoblast. 

 A:. Cavity formed by the separation. 



B. Completion of the process, and formation of 

 a germ area, or gastro-disc, of two layers 

 one (e) of epiblastic cells, the other (/) of 

 hypoblastic cells. 



OF THE EMBRYO. The first indication of the embryo is the appear- 

 ance of a longitudinal depression or furrow, termed the medullary 

 groove (Fig. 145), and it is the sign of the appearance of the most 

 important and central of all the organs of the future animal, for in 



* In a paper read before the Royal 

 Society on March 23, 1876, Mr. E. A. 

 Schafer describes the formation of a 

 membrane in the cat's ovum between 

 the epiblast and hypoblast. This mem- 

 branous follicle he named memlrana 



limitans hypdblastica. The fact of its 

 presence favours the view according to 

 which the mesoblast is derived from the 

 epiblast. See Pro. Roy. Soc., vol xxiv., 

 plate 10. 



