CCELOM AND VASCULAR SYSTEM IN THE LEECH. 481 



The evidence brought forward in this paper is derived from 

 two sources : firstly, from some injection experiments ; secondly, 

 from the study of serial sections. The former researches were 

 carried on last summer, with the help of my friend Mr. L. J. 

 Picton ; the part dealing with injections must, therefore, be 

 considered as the joint work of Mr. Picton and myself. For 

 the remainder of this paper I am alone responsible. 



The Evidence of Injections. 



Two reasons may be assigned why the work of Gratiolet, 

 Jaquet, and others has not carried conviction. These natu- 

 ralists, who, as I have already remarked, aimed rather at 

 tracing out the distribution of the hsemolymph channels than 

 settling the question of the communication between sinus and 

 vessel, do not seem to have taken any special precautions 

 against the forcing of the injected fluid through any thin walls 

 which might be supposed to separate the two systems, nor do 

 they appear to have been careful as to the state of preservation 

 of the leeches they injected. Gratiolet, indeed, frequently 

 macerated his leeches before injecting them, finding the process 

 easier to accomplish when the animals had begun to decay. 



For these reasons we determined to avoid, as far as possible, 

 all such sources of error. 



The leeches, before injection, were not killed, but anaesthe- 

 tised with a mixture of chloroform, ether, and alcohol ; then 

 spread out on a cork, and opened up so as to expose the lateral 

 vessel, by means of which the injection is accomplished. 

 When necessary, the leech, was kept in the anaesthetised state 

 for any length of time by placing on its head a pad of cotton 

 wool dipped in the anaesthetic. 



A filtered solution of Berlin blue was used for injecting, and 

 the apparatus consisted of a very fine glass cannula fixed to a 

 long india-rubber tube leading to a small funnel, into which the 

 solution was poured. The pressure of the fluid and the flow 

 from the nozzle of the cannula could be regulated at will by 

 fixing the funnel at any given height. The pressure used was 



