THE DEVELOPMENT OF AMPHIOXUS 



from branches of the posterior cardinal veins, which divide the 

 germinal epithelium into dorsal and ventral portions. Inside 

 the gonad is a space known as the primary ovarian or peri- 

 go nadial cavity, in the outer wall of which the definitive germ 

 cells are developed. Out- 

 side the gonad, and sepa- 

 rating it from the atrial 

 epithelium and body wall 

 proper, is a secondary 

 ovarian cavity or gono- 

 coel. In the wall of the 

 gonocoel, just above and 

 below the stalk of attach- 

 ment through which the 

 blood-vessels pass, are 

 thickened patches in the 

 atrial wall of the gono- 

 coel the dorsal and ven- 

 tral cicatrices. During 

 the later stages of their vg~\ 

 formation the germ cells 

 oogonia or spermatogo- 

 nia, enlarge so consider- fe 

 ably as nearly to oblit- f 

 erate, by compression, 

 these cavities and even to 

 cause the gonads to en- 

 croach very considerably 

 upon the atrial cavity. 



Toward the end of the 

 growth period the nucleus, 



vg 



which contains a large 



FIG. 3. Diagram of a section through 

 the gonad of Amphioxus. After Cerfon 

 taine. 6, Peribranchial (atrial) epithelium; 

 c, cicatrix; /, true follicular epithelium; fe, 

 external layer of follicular epithelium; g, 

 gonocoel; ge, germinal epithelium; 01, pri- 

 mary ovarian cavity; 02, secondary ovarian 

 cavity; pg, 'parietal layer of gonocoel; v, car- 

 dinal vein; vg, visceral layer of gonoccel. 



nucleolus, passes through 



the synizesis stage and 



the deutoplasm granules, whose formation began toward the 



inner side of the oogonia when these were only about 0.05 mm. 



in diameter, crowd the entire cell body except in the perinuclear 



