INTERNAL ANATOMY. 



25 



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 Fig- 9- — Amphioxus dissected fiom 

 T _. . . the ventral side. (After Rathke, slightly 

 anus. In l^lg. 9 the position altered.) 



of this pOSt-atrioPoml exten- . "': E"fance to mouth with the buccal 



^ ^ cirn lying over it. p. Pharyn.x. c. Endo- 



SlOn of the atrium is indi- style. /. Hepatic co^cum. i;. Gonadic 



, 1 r 1 1 pouches, at. Position of atriopore ; the 



Catecl by means Ot a dotted post-atrioporal extension of the atrium is 



]|j^g indicated by the dotted line passing over 



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



Finally, in Fig. 9, the anus Anus. 



1 . , ,,,-.. N.B. — Note absence of differentiated 



is seen lying to the left of stomach. 



* The crecum is held in position by cord-like attachments to the ligamen- 

 tum denticulatum. 



