INTERNAL ANATOMY. 



anastomosing of the branch- 

 es, etc. It is essentially a 

 median ventral outgrowth 

 from the intestine, and its 

 lying on one side of the 

 pharynx in Amphioxus is 

 only a secondary topographi- 

 cal necessity.* 



Attached to the lateral 

 muscular body-wall on each 

 side are the gonadic pouches, 

 which project into the cavity 

 of the atrium. (Cf. Fig. 2.) 

 Their number, which is usu- 

 ally twenty-six pairs, varies 

 slightly, and sometimes there 

 are more on one side than 

 on the other, as in Fig. 9. 



The atrial cavity does not 

 end at the atriopore, but is 

 continued beyond it as a 

 blind sac lying to the right 

 of the intestine, and reach- 

 ing back nearly as far as the 

 anus. In Fig. 9 the position 

 of this post-atrioporal exten- 

 sion of the atrium is indi- 

 cated by means of a dotted 

 line. 



Finally, in Fig. 9, the anus 

 is seen lying to the left of 



* The coecum is held in position 

 turn denticulatum. 



m 



\ 



-an 



Fig. 9. Amphioxus dissected from 

 the ventral side. (After RATHKE, slightly 

 altered.) 



m. Entrance to mouth with the buccal 

 cirri lying over it. /. Pharynx, e. Endo- 

 style. /. Hepatic caecum, g. Gonadic 

 pouches, at. Position of atriopore ; the 

 post-atrioporal extension of the atrium is 

 indicated by the dotted line passing over 

 to the right side of i, the intestine, an. 

 Anus. 



N.B. Note absence of differentiated 

 stomach. 



by cord-like attachments to the ligamen- 



c> 



