4 H. F. NIEESTEASZ. 



in different forms and doubts its existence (17, pp. 268 and 315). 'As has been 

 indicated by me elsewhere, the existence of a basal membrane has to be accepted for 

 several forms (9). The membrane is stained red with carmalum, consequently its 

 structure differs from that of the chitinous teeth. Probably it must be considered 

 as a cuticle, and so its origin is entirely different from that of the radula-teeth, which 

 are formed in the distal portion of the radula-sac by large odontoblasts. In this 

 respect Promomenia discoveryi resembles those forms, already described by me 

 elsewhere (9). So we have to do here with a multiserial radula with basal membrane. 

 Of any double character of the radula, viz., of the existence of a right and a left 

 half, no trace is to be found. The distal portion of the radula-sac, however, is 

 divided into two parts, a right and a left one (Figs. 10, 20) ; in both parts radula- 

 teeth are formed by a thick cushion of odontoblasts. Here also the radula originates 

 from the coalescence of a right and a left portion. 



The wall of the cone and the dorsal wall of the ventral pouch consist of 

 epithelial cells with round nuclei, between which numerous extremely slender 

 supporting cells occur with elongated nuclei (Fig. 16). On the ventral wall of the 

 ventral pouch and on the dorsal wall of its distal end supporting cells are absent ; 

 this ventral wall is formed by cylindrical epithelium with oval nuclei, whilst the 

 constituent cells of the dorsal wall of the distal portion are higher and more 

 cylindrical. One part of this dorsal wall more especially deserves notice ; the distal 

 and median part is invaginated and of an entirely different structure. Here very long 

 and slender cells are found, with pointed nuclei and granular contents. It leaves the 

 impression that these cells have pushed themselves wedgewise between the epithelial 

 cells; yet no sharp line can be drawn between these two elements (Fig. 18). Upon 

 this wedge-shaped part the proximal rows of the radula-teeth are resting ; the basal 

 membrane, however, fails here. As to the significance of this wedge I am at a loss. 

 There seems to be a connection between the wedge and the layer of muscular and 

 connective tissue surrounding the radula-sac, numerous fibrils pushing themselves 

 between the cells of the wedge. I am bound to mention its existence, having found 

 in a similar ventral pouch containing the proximal portion of the radula in Proneomenia 

 weberi, a regeneration either of the cuticle or of the radula (6, p. 4). But in this 

 new form I do not believe we have to do with a regeneration ; its significance remains 

 undecided. 



Still, in another respect the ventral pouch is of great importance, as the 

 salivary glands open into it (Figs. 11 and 15 5^). These are tube-shaped, and extend 

 a long way distally ; they merge separately into the ventral wall of the ventral 

 pouch. 



The connective tissue and the muscles, which are in connection with the radular 

 apparatus, are strongly developed. Ventrally and laterally from the radula-sac 

 numerous crystal-clear cells occur ; usually these are small, sometimes, however, of 

 large size (Fig. 10 cc). They serve as a support for the surrounding connective 



