HOUGHTON, ON THE GLOSSIPHONlDiE. 37 



red blood, but it was a common tbing to remark that speci- 

 mens of about three lines long, and seven or eight weeks 

 old, had their digestive system thus beautifully coloured. 

 The subject is worthy of further investigation. 



The circulation in the Glossiphonidae may be most readily 

 watched in the young of any of the species, and in adult 

 individuals of G. bioculata and G. hyalina, but from the 

 transparency of the circulating fluid, and from the com- 

 plexity of the vascular system, with its numerous network of 

 vessels which communicate with the dorsal and lateral ones, 

 it is extremely difficult to make out with satisfaction the 

 true and complete course of the vital fluid. This much, 

 however, I have been able to notice. There is a large and 

 tortuous dorsal vessel, a ventral vessel, two lateral vessels, 

 with innumerable other small ones, which form almost a 

 netM^ork of communication between the grand central and 

 lateral canals. The dorsal vessel is furnished, at intervals, with 

 valve-like processes, which are arranged alternately on either 

 side of it ; it is contractile and heart-like in its functions. 

 This group thus diff'ers in a very important particular from 

 the true leeches which form the genera Hirudo, Htemopis, 

 Aulostoma, Trochetia, and Nephelis, in all of which the 

 side vessels, arid not the dorsal, are contractile, and act the 

 part of a heart. I have carefully studied the mechanical 

 action of these valve-like processes alluded to above, and 

 believe that they are designed to propel a large portion of 

 the vital fluid to the sides ; this they do by partly closing a 

 section of the dorsal vessel, and thus stopping a certain quan- 

 tity of the blood from flowing up it; this section of the 

 dorsal vessel contracts and forces a portion of the blood into 

 the numerous branching channels which communicate with 

 the dorsal and lateral vessels ; indeed, the dorsal vessel may 

 be considered to consist of several hearts, each one of which, 

 so far as its functions are concerned, being formed by the 

 space included by the valves, which, simultaneously with the 

 contraction, swing on their narrow bases, by which they 

 are attached each to the opposite side of the dorsal vessel, 

 and thus partially close it, not entirely, however, for even 

 when the valves are closed corpuscles may be seen to pass 

 through the nari-ow portal from one of the dorsal cham- 

 bers to another; in this manner a large portion of the 

 blood 'finds its way through the intercommunicating chan- 

 nels to the grand lateral vessels, for the purpose, as will be seen 

 by and by, of becoming oxygenated. F. Miiller [' De Hiru- 

 dinibus circa Berolinum observatis') supposes these valves 

 are merely intended to prevent the vital fluid from flowing 



