ii6 



DEVELOPMEXT OF AMPHIOXUS. 



of the first myotome, extending from the right side under- 

 neath to the left side of the body. (Cf. Figs. 63 A and 71.) 

 The groove deepened, and its margins coalesced, and so it 



Fig. 63. — Grow-th of the ciliated embryo of 

 Amphio.xus. (.\fter Hatschek, slightly altered.") 



A. Stage, with nine pairs of myocoelomic pouches ; 

 from left side. 



B. Same stage from dorsal side. 



C. Stage, with fifteen pairs of myotomes; from 

 the right side. Vacuoles have appeared in cells of 

 notochord. 



ch. Notochord. c.s.g. Club-shaped gland, .f.j. 

 Rudiment of first gill-slit. int. Intestine, l.a.d. Left 

 head-cavitv (left anterior intestinal diverticulum). 

 viwc. Mvocoelomic (archenteric) pouches. 7ip. Neu- 

 ropore. n.t. Medullary tube. pi^. Pigment granules 

 in floor of medullary tube, p.n.c. Posterior neuren- 

 teric canal, r.a.d. Right head-cavity (right anterior 

 intestinal diverticulum). 



~p:n.e 



became constricted from the gut, and now forms a hollow 

 sac closed at present at both ends. It is known as the cliib- 

 sliapcd gland. Immediately behind it, in Fig. 63 C is seen 



