DEVELOPMENT 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. Growth of the ciliated embryo of 

 Amphioxus. (After 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, g.s. 

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

 head-cavity (left anterior intestinal diverticulum). 

 my.c. Myocoelomic (archenteric) pouches, tip. Neu- 

 ropore. n.t. Medullary tube. pg. Pigment granules 

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

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

 intestinal diverticulum). 



became constricted from the gut, and now forms a hollow 

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

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



