CONTRIBUTIONS TO TEE ANATOMY OF THE HIRUDINEA. 459 



ing of this communication, as I am uncertain whether in this 

 instance Vaillant had hold of the lateral vessel or lateral 

 sinus, or indeed of the dorsal vessel or dorsal sinus. The 

 inference I draw from his description is, that there is a 

 communication from the lateral vessel to the dorsal sinus. 

 This seems improbable, since no other leech presents any 

 such arrangement. If, however, it passes from the lateral vessel 

 into the dorsal vessel, it is no anomaly, and with due reserve I 

 may suggest these to be its relations. 



Around the lateral (longitudinal) vessel lies what I have called 

 above a lateral sinus ; this is never really developed as a sinus 

 around the lateral vessel, but there is a looseness about the con- 

 nective tissue outside the muscular wall of the vessel, and a con- 

 siderable amount of blood in the region, and — a fact which seems 

 to me to possess great weight — there exist around the lateral 

 vessels muscular bands, three to every somite, which recall the 

 muscular bands described above as occurring in the wall of the 

 dorsal sinus (fig. 46, m.). I consider that we have here the 

 remnants of a lateral sinus which surrounded the lateral vessel, 

 as the dorsal sinus surrounds the dorsal vessel (woodcut fig. 2, 

 /. V. and /. s.). 



As stated above, no branches pass from the lateral vessel to 

 the body ; there are, however, a series of small branches 

 (branchial vessels) which, passing through the muscular layers, 

 open into dilatations lying in the subepidermic region ; these 

 dilatations communicate, on the other hand, by a sinus (bran- 

 chial sinus) with the " lateral sinus '' ; the degenerate condition 

 of the latter is quite in accordance with the condition of these 

 lateral dilatations. Blood passes from the lateral vessel into these 

 vesicles, and then into the sinus (figs. 8 and 64, br. v., br. s.). 



In Pontobdella certain other very interesting vascular de- 

 velopments occur, which require further investigation. They 

 are rounded bodies, occurring along with the deep-lying clitellar 

 gland-cells, and of about the same size. They present a more 

 or less definite capsule (fig. 44, o), formed by a close packing of 

 elongated connective-tissue cells. In certain spots there is free 

 communication with blood spaces (fig. 4, m. n.). The capsule. 



