304 



CHORD AT A. 



AmphioAus is dioecious. I'he gonads lie as a paired 

 Reproductive ^^^^^^^ ^^^ <^f organs just inside the ventral 

 ■ longitudinal muscles. They are said to have 

 no ducts and to burst into the atrium when ripe. 



Fig. 218.— The Development of Amphioxus as seen in Longi- 

 tudinal Section and Lateral View of Larv/E. 

 A B 



Blastopore. 



Hypoblast. 



Note chord. 



Blastopore 



Neurenteric 



Canal 



Notochord. 



5 Neuropore. 



I 



4 6 



Neural Tube. 7 Neuropore. 



Anterior Meso- 

 blastic Sac. 



! "^ Collar-sac, followed by 



8 the Mesoblastic Somites. 



\ Blastula B Gastrula. C, Completed Gastrula. D, Commencing Neural Tube. 

 E and F, Lateral view of later chord ula stages. (After Hatschek.) 



