PHAEYNX. 



21 



is an organ for creating currents in the mouth back to the 

 pharjTix. The preoral pit which opens into its front part 

 has been variously interpreted as a sensory organ and a gland. 



If the preoral (Hatschek's) pit be regarded as a gland, it has been sug- 

 gested by V. Wijhe that it is comparable to the neural gland of the Tunicata, 

 and that the ciliated groove is comparable to the opening of that gland, 

 the dorsal tubercle, the edges of which are frequently drawn out in a manner 



-20 



-19. 



-17 



Fig. 9. — Transverse section through the middle of the buccal cavity of A mphtaxtislanceolatus 

 to show the preoral (Hatschek's) pitaudtlie ciliated furrow (after v. Wijhe). 1 Hatschek's 

 pit ; 2 ri;?ht side of preoral hood ; 3 outer Up-cavity ; 4 inner lip cavity (3 and 4 are parts 

 of the left collar somite of the embryo) ; 5 labial nerve ; 6 coelom (dorsal buccal, a portion 

 of the collar somite of the embryo) ; 7 contorted blood vessel (continuation of right aorta) ; 

 9 aorta ; 10 Hatschek's nephridium (a process from the pharynx) ; 11 buccal cavity ; 12 

 internal labial muscle ; 13 skeleton of cirrus ; 14 cavity (lymph space) of cirrus ; 15 exter- 

 nal labial muscle ; 17 left side of preoral hood ; 18 second, 19 third, 20 fourth myotome. 



very similar to the course of the ciliated groove of Am-phioxus. Against 

 this interpretation we must set the fact that the preoral pit, whatever 

 its origin (see below), has no relation to the central nervous system. 

 Moreover the interpretation of it as a gland is a very doubtful one. Van 

 Wijhe describes a special part of the ciliated furrow just behind and in 

 close connection with Hatschek's pit as the ciliated 'pit (Fig, 8, 8). 



The pharynx is a large chamber tapering slightly posteriorly 

 on account of the dorsal inclination of its ventral wall. Its side 



