THE ANATOMY OE THE LEECH. 27 



NOTES ON SOME POINTS IN THE ANATOMY OF 

 THE LEECH. 



BY JAMES BOYELL, M. D. 

 PROCESSOR OF TIIE INSTITUTES OF MEDICINE, TRINITY COLLEGE, TORONTO. 



Read before the Canadian Institute, December 15tJi, 1855. 



Duges, Home, Jones, and other distinguished anatomists, in their 

 descriptions of the structure of the Leech have assigned to certain 

 highly developed parts in this Annelid, functions which it was bv no 

 means clear to many more recent observers, could legitimately be 

 performed by them. It Avas reserved, however, for Dr. Williams, of 

 Swansea, a highly distinguished comparative anatomist, to unravel the 

 mystery, and to furnish proof of the errors into which his predeces- 

 sors had fallen. 



The existence of an elaborate circulating system seemed to necess- 

 itate an aerating one equally developed in character ; but spiral ves- 

 sels, on the type of insecta, no where being seen, the vascular- 

 walled pouches, occupying the lateral regions of the body, seemed to 

 be the organs of respiration, supplied freely with blood by vascular 

 hearts. While many doubted the existence of so special an organi- 

 zation for respiration in this creature as was described, no one before 

 Dr. "Williams had assigned them to the generative apparatus, and as I 

 believe that the observations which have been repeated here confirm 

 the results arrived at by the Naturalist of Swansea, I thought it of suf- 

 ficient interest to bring the subject before the Institute. I cannot, 

 however, agree with Dr. Williams that the generative organs are 

 rightly described, even by himself. In order to understand the sub- 

 ject, as now unfolded to us, it may be more advantageous to state the 

 opinion of one of the highest authorities. 



Mr. Jones, in his ''Animal Kingdom," observes: "Two lateral 

 Is are appropriated to the supply of the respiratory system, and 

 in them the blood moves in a circle quite independent of that formed 

 by the dorsal artery and ventral vein, although they all communicate 

 freely by means of cross branches, those passing from the lateral ves- 

 Bels to the dorsal being called by Dugos dorso-lateral, while those 

 which join the lateral trunks to the ventral canal are the latero- 

 abdominal branches. The movement of the blood in the lateral or 

 b< patera of vessels is quite distinct from that which is 

 ace- in the dorso-vontral system or systemic. 



ixamining one of the respiratory pouches, its membranous 

 wall i en to be covered with very Que vascular ramifieatii 



from two sources; the latero»abdomina] ' off 



