C(ELOM AND VASOUTiAR SYSTEM IN THE LEECH. 477 



On the Communication between the Coelom and 

 the "Vascular System in the Leech, Hirudo 

 medicinalis. 



By 



Edii^in S. Croodricli, B.A., 



Aldrichian Demonstrator of Comparative Anatomy, Oxford. 



With Plates 42—44. 



Contents. 



PAGE 



Introductory ...... 477 



The Evidence of Injections .... 481 



The Evidence of Sections. .... 482 



Summary and Conclusion ..... 490 



The investigation, of which an account is given in the 

 following pages, was undertaken with the object of ascertaining 

 for certain whether, in the medicinal leech, the cavities of the 

 so-called sinus system do, or do not, communicate with those of 

 the contractile vascular system. 



This question, which at first sight seems so simple, has for 

 many years given rise to much controversy, some authors 

 believing the communication to exist, others, on the contrary, 

 holding the view that the two systems of cavities are quite 

 distinct. Since the champions of neither theory have brought 

 forward conclusive evidence in support of the view they uphold, 

 the question remains to this day unanswered. 



Several reasons have tended lately to arouse renewed interest 

 in the relations of the vascular system of the leech, and to 



