CONTEIBUTIONS TO THE ANATOMY OF THE HIRUDINEA. 463 



enough, but that they open directly into the lateral sinuses I 

 very much doubt. 



2. Leydig figures only eleven pairs of sinuses communicating 

 between the ventral and the lateral sinus, Whitman about 

 twenty, and Budge some sixty-two pairs of such sinuses, only 

 the last-mentioned observer not recognising the median ventral 

 sinus figures these as running from one lateral sinus to the other. 

 My own observations are not clear upon this point. While in- 

 jecting Clepsine with mercury from the ventral sinus I have ob- 

 served the mercury pass forwards and instantly fill the dorsal sinus 

 and afterwards the lateral sinuses, the mercury has then appeared 

 in about 120 very superficial sinuses which run directly trans- 

 versely ; these appear not to be filled directly from the lateral 

 sinuses and to fill in alternate directions, one filling from right 

 to left, the next from left to right, and so on. I am uncertain 

 at present as to the nature of these, but their number and abso- 

 lute regularity is very striking. It seems to me probable that 

 Budge saw these spaces, but that he counted a pair as one, 

 while Leydig and Whitman saw the more deeply-lying sinuses 

 passing from the lateral to the median ventral sinus. 



3. The above description, unless Budge be correct about the 

 vessels coming from the intestinal walls opening directly into 

 the lateral sinus, provides for no communication between the 

 vascular system and the system of sinuses. That such a commu- 

 nication exists in all leeches appears to me certain from the fact 

 that the blood presents similar characters in vessels and sinuses. 

 Although the large coelomic epithelium cells which line the 

 larger sinuses in Clepsine and Pontobdella sometimes float into 

 the blood, they never occur in the vessels — the communications 

 between the latter and the sinuses are no doubt too small to 

 allow of the passage of such large cells. The common cor- 

 puscles are of exactly the same size whether they occur in the 

 one system or the other, and although no communication is 

 obvious in Clepsine, there is a strong a priori probability in 

 favour of its existence, in that, the two systems are so obviously 

 connected in the majority of Hirudinean genera. 



There are, moroever, at the lateral margins of the body a series 



VOL. XXIV. NEW SER. I I 



