482 EDWIN S. GOODRICH. 



so slight, and the tip of the cannula so fine, that the blue fluid 

 only came out drop by drop from its extremity. 



When the cannula is introduced into the lateral vessel, the 

 blue fluid mixes with the hsemolymph and spreads throughout 

 the system of channels, apparently often as much by the natural 

 contractions of the vessels as by the pressure exerted from the 

 cannula. 



A large number of such injections were made both in 

 Hirudo medicinalis and Aulostoma gulo, the operation 

 lasting from thirty minutes to twenty-four hours. The leeches 

 were then killed, hardened, and cut. 



We found that the injection from the lateral vessel of one 

 side passed easily into the lateral vessel of the opposite side. 

 It also very soon reached the dorsal and ventral, and the peri- 

 nephrostomial sinuses, and the capillary networks of the body- 

 wall. On the other hand, it seemed to penetrate into the 

 botryoidal channels only with some difficulty, and in the last 

 place. 



Transverse sections show all these spaces filled with haemo- 

 lymph tinged with the Berlin blue. The injection seems to 

 have flowed in quite natural channels, and shows no signs of 

 having been forced into spaces not belonging to the contractile 

 and non-contractile systems, or through thin walls of sepa- 

 ration. 



In fact, we fully convinced ourselves that, both in Aulostoma 

 and in Hirudo, blood-vessels, sinuses, and botryoidal 

 tissue are in free communication. At the same time we 

 realised that the evidence of injections alone can never be 

 placed entirely beyond criticism, and that some other method 

 would have to be adopted to convince the sceptical, and remove 

 all possibility of doubt. 



The Evidence of Sections. 



A careful reconstruction of a series of sections seemed to nie 

 the only way of obtaining the end in view. The method I 

 adopted was as follows. Having anaesthetised the leeches. 



