THE NEMERTINI 



175 



cases, the stomodaeum is formed in the blastoporal region. 

 The enteron is in Carinella a simple cylindrical tube, which be- 

 comes slightly constricted, at intervals, by the developing gonads ; 



71 -- 



a--- 



FIG. XII. 



Diagrammatic sagittal section of Amphiporus, to show the median, anterior, intestinal 

 diverticulum (m) of the Metanemertines. a, rhynchostome ; b, rhynchodaeum ; c, cavity of the 

 proboscis ; d, muscular wall of proboscis ; e, rhyuchocoel ; /, dorsal cerebral commissure ; 

 g, ventral cerebral commissure; h, mouth; i, buccal tube ; j, "stomach"; k, pylorus tube; 

 I, intestine ; m, anterior caecum ; s, muscular wall of rhynchocoel. 



in Carinina and Cephalothrix these constrictions are more definite ; 

 while in the rest of the class longer or shorter pouches or 

 diverticula are formed, which in some cases may even branch; 

 they are separated from one another by dorso-ventral muscles 

 forming more or less complete septa. There thus comes about a 

 kind of metameric segmentation not only of the enteron itself but 

 also of other organs, such as the gonads, which alternate with 



FIG. XIII. 



MalctcoMella grossa O. F. Mullet (after von Kennel, Oudemans, and Burger), a, the 

 mouth (dorsally situated), which is common also to the proboscis ; b, the great "foregut" 

 or "stomach" ; c, the pylorus tube ; d, the intestine ; e, rhynchostome, opening into the roof 

 of the stomodaeum ; /, proboscis ; g, gonads ; h, sucker ; i, excretory pore ; j, dorsal blood- 

 vessel ; k, lateral blood-vessel. The figure on the left is seen from the ventral surface ; the 

 middle one from the dorsal ; it illustrates the vascular and the excretory systems the latter 

 is indicated on the right side only, and here a part of the lateral blood-vessel has been 

 omitted ; the left excretory duct and pore are shown. 



these pouches. Only in Malacobdella is the intestine a simple tube, 

 unconstricted by the gonads, and taking an undulating course from 

 mouth to anus (Fig. XIII.). The anus is always small and terminal. 



