4 Mr. C. Robertson on the Organs of 



to make a perfect injection of such delicate animals without 

 some extravasation. If these two examples are placed side by 

 side, and a comparison made of the vascular system, it is quite 

 obvious that in the first example the injection had only filled 

 the venous system, and left the arterial quite empty. Injection 

 performed in this way fills first large spaces in the body, then 

 the venous capillaries of the viscera, and lastly the pulmonary 

 capillaries, before it reaches the heart ; and a good deal of pres- 

 sure is required to get it thus far. In the second experiment 

 the injection was thrown into the natural starting-point of the 

 circulatory current; and, for the present, I attach great import- 

 ance to the fact of the whole vascular system being well filled, 

 and only a small quantity of extravasation being found, round 

 the nerve-collar, — most likely the result of a little too much 

 pressure on the syringe. 



The heart of the snail consists of a single auricle and ventri- 

 cle enclosed in a pericardium (PL I. fig. 2 a), which is situated 

 at the posterior and left extremity of the pulmonary chamber, 

 about the middle of the lower border of the kidney (fig. 2e). 

 The delicate auricle receives the blood by a large pulmonary 

 vein (fig. 2 b) from the surface of the pulmonary sac and kidney, 

 and propels it into the ventricle, which is situated behind it and 

 on the same plane. The aorta (fig. \ j), after leaving the ven- 

 tricle, perforates the peritoneal covering of the viscera, and passes 

 into the abdominal cavity between a loop of intestine and the 

 anterior margin of the liver, with the receptaculum seminis closely 

 adhering to its right surface. It soon gives off two trunks 

 (fig. 1 k) for the posterior part of the crop, the liver, and the 

 whole of the viscera placed in the spire of the shell. The first 

 of these trunks is the largest, and gives twigs to that part of the 

 digestive tract contained in the spire of the shell. The second 

 of these branches is much smaller, and is lost on the posterior 

 portion of the crop and the albuminiparous gland and that part 

 of the intestine which runs along the side of the pulmonary 

 chamber. The aorta, after giving off these branches, bends for- 

 wards, having the crop on its inferior surface and the conjoined 

 generative ducts above it. The next trunk which proceeds from 

 it is a stout branch, and is given off when the aorta in its for-» 

 ward course reaches the posterior and right extremity of the 

 salivary gland. This trunk again breaks up into three branches, 

 which all spring from the same point. The first branch (fig. 1 /) 

 passes to the right and supplies the sides of the body, and then 

 passes down and is lost in the upper portion of the foot. The 

 second branch runs to the left (fig. 1 n), and is lost on the sur- 

 face of the crop and salivary glands. The third branch (fig.l?/z) 

 passes straight down between the retractor muscles of the head, 



