182 Transactions. 



regard each as single. In front of the eyes are two annuli, both 

 of which are strongly bent so as to be V-shaped in this indi- 

 vidual. Thf; ocular annulus is thus the 3rd ; the 4th shows 

 indications, especially laterally, of being double ; the 5th is 

 the first complete one, and forms the posterior margin of the 

 anterior sucker : this also presents an indication of being 

 double. 



There appear to be 70 annuli — possibly 71 or even 72; but 

 the posterior region is so much contracted that I did not find it 

 possible to distinguish annuli certainly from the wrinklings on 

 the base of the sucker. 



The anus is on the 69th annulus. 



The papillae above referred to are on annuli 6, 9, 12 &c., 

 63, 68, 69, and I believe on 70 and 71, which are at base of the 

 sucker and form its dorsal surface here. There are, thus, 

 normally three annuli to a somite. In the greater part of 

 these annuli there are four papillae — a pair dorsally and a 

 pair dorso-laterally placed. They are nearly equidistant from 

 each other, but the space between the dorso-lateral and the 

 margin of the leech is about half that separating the dorsal 

 from the dorso-lateral (figs. 2, 3). Owing to the great con- 

 traction of the two extremities I was unable to detect the 

 outer papillae on annuli 6, 9, or 68, 69. 



Turning now to the ventral surface, the anterior sucker 

 is bounded posteriorly by the 5th annulus. The mouth lies 

 rather low down on the anterior lip, and was only recognisable 

 in sections. The true form of this anterior sucker is concealed 

 by the contraction of the leech, the upper lip being curved 

 downwards so as to reduce the opening to a narrow crescentic 

 slit. 



The male pore is a rounded prominence (? due to contrac- 

 tion) between the 25th and 26th annuU {i.e., 21st and 22nd post- 

 oral). The female pore, detected only in sections, lies two 

 annuli behind — i.e., between the 27th and 28th. 



Following Castle (8), who finds in the Glossosiphonids, exa- 

 mined by him with great care, that the anterior sucker is 

 always contained in the somite iv, we have the male pore 

 between somites xi and xii, while the female pore is between 

 annuli h and c of somite xii. It is the presence of these two 

 annuli between the pores that is used as one of the charac- 

 ters of Placobddla by Blanchard (4, 6). 



Internal Anatomy 

 The internal anatomy was studied by means of longitudinal 

 sections. 



The Alimentary Tract (fig. 4). — The mouth is small, situated 



