318 ARTHUR WILLEY. 



the same relation to the neuropore as the dorsal tubercle does 

 to the ueuropore in the Ascidians (cf. fig. 14, PL 1). The 

 only conclusion to be drawn from this is that Kolliker's olfac- 

 tory pit in Amphioxus is homologous with the proximal 

 portion of the hypophysis duct in the Ascidians, while the 

 glandular portion of the hypophysis is unrepresented in 

 Amphioxus. 



Hatschek (I, 16), if I understand him aright, has curiously 

 enough suggested that the dorsal tubercle of the Ascidians — 

 that is, the opening of the hypophysis duct into the stomo- 

 dajum — is homologous with the prseoral pit of Amphioxus; 

 while the glandular portion of the Ascidian hypophysis, or the 

 " Neuraldriise," would be homologous with the olfactory pit 

 (Flimmergrube) in Amphioxus, the two portions of the hypo- 

 physis being in the latter separated from one another by the 

 notochord. Judging from a recent publication (3), in which 

 Hatschek makes the prseoral pit of Amphioxus a gill-slit, he 

 would seem to have somewhat modified his original view, 

 which was based largely on observations made by Herdman 

 (4) on Ascidia mammillata, in which, while confirming 

 Julin's discovery that in this species the neural gland, besides 

 having the usual duct running anteriorly to communicate with 

 the pharynx by the dorsal tubercle, has also a number of short 

 funnel-shaped apertures into the peribranchial cavity, he adds 

 that in two specimens examined by him the duct of the hypo- 

 physis had no opening into the pharynx, the dorsal tubercle 

 being entirely absent. Herdman, therefore, suggested that 

 the dorsal tubercle and neural gland represent originally dis- 

 tinct structures, which in most Ascidians have acquired a 

 secondary communication with one another. This view, which 

 receives only the slenderest support from the facts intended to 

 establish it, is obviously untenable in the light of what has 

 been said above as to the origin of the respective structures. 



In 1870, several years before Ussow discovered the con- 

 tinuity of the dorsal tubercle of the Ascidians with the sub- 

 neural gland, Ganin, in studying the development of Di- 

 demnum (Diplosoma) gelatinosum, found that the cavity 



