17 



things which existed forty years ago. It is a pity that M. Jaquet did 

 not take the trouble to make himself more thouroughly acquainted with 

 the previous literature upon the subject. My own »Contributions to the 

 Anatomy of the Hirudinem are treated in a very off-hand manner. They 

 are mentioned in one place only, and that in connection with Pon- 

 tohdella, here, M. Maurice Jaquet having discovered that I actually 

 believed that there was »un sinus dorsal, emprisonnant le vaisseau 

 dorsal« appears to have given up any attempt to read further what I 

 had to say. The statement qvioted is however correct, and further, it 

 embodies the keynote to the whole of my views regarding the blood 

 spaces found in leeches viz. that there are in all leeches two systems of 

 spaces which contain blood and that although these communicate one 

 with the other, the one system (vessels) represents the closed vascular 

 system of Ghaetopoda, while the spaces (sinuses, capillaries and botry- 

 oidal spaces) of the other system represent collectively, coelom. I lay 

 no claim to having originated,^this theory, I merely followed in the foot- 

 steps of Ley dig. De Quatrefages and Whitman. Leydig and 

 subsequently Whitman recognised the existence of the two systems 

 and De Qu atre fag e s went further and compared one of the systems 

 to the closed vascular system in Chaetopoda I arranged, the facts pre- 

 viously established and my own observations, in such a way as to place 

 the theory upon what seemed to me a very satisfactory basis. But M. 

 Maurice Jaquet will have none of it, the words sinus and vessel 

 have no separate meaning for him, with this result, that the inter- 

 pretations that he himself puts upon the facts which he has discovered 

 are unintelligible, while I read in his facts confirmations of the theory 

 stated above and have little doubt but that if M. Jaquet with his 

 marvellous skill in injecting would reexamine certain points of detail 

 that we should know the whole truth. I proceed to point out a few of 

 the most interesting questions. 



Hirudo. M. Jaquet confesses himself unable to find any direct 

 communication between the lateral vessels and the dorsal sinus al- 

 though he is satisfied that communication exists , so am I , but not a 

 direct communication, it is through the intervention of capillaries or 

 botryoidal tissue spaces into which numerous small vessels open and 

 these together with the ventral sinus form part of the coelomic space. 

 Again he recognises the difficulty of shewing exactly how the lateral 

 vessels communicate with the dorsal sinus. Indeed nowhere in his 

 exact and elaborate description of the blood channels in this genus 

 does he contradict any of my statements while nothing that he adds 

 militates against my interpretation of the facts. 



Aulostoma. I devoted but little time to this genus, my state- 



