1 62 . THE AMPHIOXUS. 



gill-slit. The opening, which at first is small (Fig. 62), 

 lies immediately underneath the region of the noto- 

 chord, on the left side of the body. The opening soon 

 enlarges very considerably. 



The ciliated duct of the club-shaped gland per- 

 forates on the upper surface of the body, somewhat 

 ventralwards from the anterior edge of the mouth. 



The perforation of the anus follows later than that 

 of the other organs mentioned here. Its place is the 

 posterior end of the alimentary canal. 



In this place there was, a short while previously, 

 to be observed a connexion of the cavity of the 

 archenteron, not only with the neural canal, but also 

 with the cavity of the mesoblast folds, and with 

 the slit of the notochord. After the mesoblast folds 

 and the notochord foundation have completely separ- 

 ated from the archenteron, there only now exists 

 the connexion with the ventrally curved end of the 

 neural canal. The two canals, which are histologi- 

 cally plainly distinguishable through the size and 

 clearness of the cells, have as their point of connexion 

 the morphological posterior end. On both sides of 

 this point are found the posterior pole cells of the 

 mesoblast folds. 



