248 



ZOOLOGY 



r.ov - 



Lord 



r.ovd 



l.ov 



r.ov 



FIG. 922. Ceratodus forsteri. Reproductive organs of female ; 

 the inner surface of the right and the outer surface of the left 

 ovary shown, cod. ap. coelomic aperture of oviduct ; liv . portion 

 of the liver ; 1. ov. left ovary ; I. ov'. its posterior termination ; 

 1. ovd. left oviduct ; r. ov. right ovary ; r. ovd. right oviduct ; 

 r. ov'. its posterior termination. (After Gunther.) 



SECT. 



remaining open 



(D) and subse- 

 quently giving 

 rise to the anus. 

 During its in- 

 crease in size the 

 blastopore has 

 been growing 

 over towards the 

 dorsal side, and 

 when its lips be- 

 come united, it 

 extends along 

 the greater part 

 of the dorsal 

 surface. A nar- 

 row medullary 

 groove (E, blp. 

 sut.) appears 

 along the dorsal 

 surface, and a 

 pair of medullary 

 folds are seen at 

 the sides of this 



(E) and are coal- 

 escent in front 

 of it. From the 

 medullary folds 

 and the groove 

 between them 

 the neurocoele, 

 and subsequently 

 the entire ner- 

 vous system, are 

 developed as in 

 Craniata in 

 general (see 

 p. 95). The por- 

 tion of the 

 blastoderm des- 

 tined to give 

 rise to the em- 

 bryo becomes to 

 a slight extent 

 folded off from 

 the rest, which 

 forms an ill- 



