MOLLUSCA. 



VII. SOLENOGASTEES. 



By Dr. II. F. NIEKSTRA--/. 

 (2 Plates.) 



THE 'Discovery' expedition brought back one specimen of Soleuogastres from 77 50' 

 30" S., 165 40' 5" E., 100 fathoms, of which Fig. 1, A gives a representation. The 

 length is 23 mm., the diameter 2 '25 mm., the index therefore about 10. Proximally 

 the animal is blunt, slightly broadened, with a slit-like mouth (Fig. 1, B). The distal 

 part terminates in a dorsal prolongation. On the ventral side the rhomboid opening 

 of the cloaca is distinctly visible, as also the ventral groove, which runs as far as that 

 opening (Fig. 1, C). The opening of the ciliated groove (" Flimmcrhohle " of Wiivn) 

 is also visible. The animal has no lustre. When slightly enlarged, spicules arc seen 

 crossing each other at obtuse angles. The colour of the animal in alcohol is a yellowish 

 brown. 



After being decalcified in nitric acid (1 per cent, in alcohol 90 per cent.) and 

 being stained in iron carmalum for twenty-four hours, transverse sections were made 

 of the proximal and distal portions for the study of the internal organs. The spicules 

 of the different parts of the body were isolated in Eau de Javelle. They ;uv small, 

 but strictly uniform. They belong to the true Proneomenia type : hollow, straight, or 

 more or less curved or S-shaped calcareous tubes, which end either sharply or bluntly 

 (Fig. 2). In some cases the base is slightly broadened. I have not succeeded in 

 finding spicules of different shapes along the ventral groove, nor at the proximal and 

 distal portions. At the proximal end, however, they are somewhat more curved. 



The spicules arc arranged indifferent layers upon each other. The whole of the 

 strong cuticle is pierced by numerous papillae. The greater part of these are oval, pear- 

 or dub-shapcd, sometimes round, and they show some transparent cells (Fig. 4). They 

 are placed on strong multiuuclear stalks, the cells of which are more or less fibrous. 

 Amongst the transparent cells granular supporting cells are found. It is worthy of 

 note that these papillae are often branched. The side-branch never readies the length 

 of the stalk, though ending also in a papilla. In most cases these epidermal papillae 

 do not open on to the exterior, but remain closed. Thielc believes the papillae to be 

 sensitive, an opinion which I share (13, p. 280). In the stalk a thin thread may 

 occur, arising from the circular muscular layer. Whether this thread is of a nervous 

 character or not remains undecided. There is. however, no penetration into the circular 



