298 



THE EVOLUTION OF MAN. 



spoken of as the "first germ-rudiment or embryonic rudi- 

 ment," as the " primitive germ," or " the first trace of the 

 embryo." But these designations, which are based on the 

 authority of Baer and Bischoff, are incorrect. For in reality 

 the germ or embryo ah^eady exists in the parent-cell, in the 

 Gastrula, and in all the subsequent germ-stages. The germ- 

 shield is merely the earliest rudiment of that dorsal part 

 which first becomes defined. 



Fig. 85. — Germ-area or germ-disc of a Rabbi b, with a sole -shaped germ- 

 shield (about ten times enlarged) . The light, circular tract (d) is the dark 

 area (a. opaca). The light area {a. pellucida) (c) is lyre- shaped, as is the 

 germ-shield itself (&). Along its axis the dorsal furrow or spinal furrow (a) 

 is seen. (After Bischoff.) 



Fig. 86. — Sole-shaped germ-shield of a Dog ("double shield" of Remak, 

 " embi'yo-rudiment " of other authors), In the centre is the dorsal furrow, 

 on either side are the spinal swellings, or medullary swellings. 



Fig. 87. — Sole-shaped germ-shield of Chick. 



After the oval germ-shield has become distinctly defined, 

 in the centre of the light germ-area, along its central line 

 a delicate, white streak appears, which soon becomes pro- 



M 



