152 



DEVELOPMENT OF AMPHIOXUS. 



of the peritoneal epithelium lining the general body-cavity. 

 The fact that they arise in the way shown by Boveri is one 

 of great morphological importance. 



In a transverse section of a young individual 5 mm. 

 in length, the primitive sexual cells are to be recognised 

 as a closely packed group of cells, with large nuclei in the 

 lower angle of the myotome ; that is, in the angle formed 

 by the membrane which divides the myoccel from the 

 splanchnocoel, which we may call the intcrccelic membrane, 

 with the cutis (Fig. 85). Since the myotomes of one side 

 alternate with those of the other, so do the centres of 



Fig. 86. Longitudinal views of the developing gonads, obtained by dissecting 

 out the ventral borders of the myotomes. (After BOVERI.) 



u.g. Primitive sexual cells arising from the myocrelic epithelium ; the nuclei 

 scattered about the surface of the preparations also belong to the myocoslic 

 epithelium. 



formation of the primitive sexual cells, and in a given 

 section, as in Fig. 85, only one such centre is to be observed 

 on the right or left side of the section, as the case may be. 

 Its actual position in the longitudinal aspect of the myo- 

 tome is shown in Fig. 86 A, B, and C. The formative 

 centres of the primitive sexual cells lie at first in the angle 

 mentioned above, but applied to the posterior faces of the 

 dissepiments between the myotomes (Fig. 86 A). 



At a somewhat later stage, having slightly increased in 

 bulk, they begin to push the dissepiments before them 



