2 Mr. C. Robertson on the Organs of 



venous systems of the Snail, and the lacunse which form the 

 means of communication between them ; but the exact course 

 which the blood takes on its way back to the pulmonary cham- 

 ber is not very definitely pointed out, or any description given 

 of the capillary system*. 



In the present paper I propose giving the result of a numerous 

 series of observations and injections of the Roman Snail (Helix 

 pomatia) ; but, before proceeding to give a detailed description 

 of the vascular system, I will describe the method adopted for 

 killing the animals, and the substances used for injecting them. 

 When the animals are killed with chloroform, spirits of wine, or 

 warm water, the foot of the animal is generally so much con- 

 tracted and rigid, that it is quite impossible to get the injec- 

 tion to run far without much of it extravasating amongst the 

 viscera. After many trials with the above and various other 

 substances, I at last found the following method of killing them 

 answer remarkably well : — Place the animal in a jar of cold 

 water, and exclude all air by placing a glass cover over the top, 

 and allow it to remain undisturbed till it is drowned, when the 

 foot will be found as fully distended and as soft and flexible as 

 when the animal is living. It generally takes forty-eight hours to 

 kill them in this way. Of injections, I have found that size 

 mixed with various colouring matters has answered better than 

 cold coloured fluids. The size, when injected very gently into 

 the vessels, clings to them, and gives a certain amount of sup- 

 port to their delicate walls. I have found the finest gelatine 

 and carmine run exceedingly well, and it has made some very 

 beautiful preparations. Cold injections have this disadvantage, 

 that, on account of the soft and flexible nature of the parts, it is 

 necessary to keep the animal in water during injection, and also 

 when it is dissected. With fluid injections, the least pressure 

 with the hand, or in lifting the animal from one dish to another, 

 may cause the fluid to escape from the vessels, or shift its posi- 

 tion ; and thus false results are obtained. When size is used, 

 and the animal is not shifted during injection or, better, till 

 the injection has set, you have an exact mould of the vessels, 

 which does not sbift its position during dissection. 



Milne-Edwards, in his experiments on the snailf, used chromate 

 of lead and size, and the injection-pipe was passed into a hole 

 made by an instrument in the base of the tentacle. Injections 

 made in this way fill first the lacunse or spaces between the 

 viscera, and finally reach the pulmonary chamber. I have tried 

 many injections in this way, and also by thrusting the injection- 

 pipe into the substance of the foot ; but I have always considered 

 it a very unsatisfactory method of proceeding ; and although it 



* Ann. des Sciences Nat. ser. 3. tome iii. p. 295. f Ibid. p. 294. 



