14 
Dr. Johnson's observations 
reproduction in almost an equal degree with the polype: but 
the experiments I have hitherto made, by no means establish 
this point. . 
In its structure the H. vulgaris closely resembles the 
H. medicinalis. At the extremity of the tail we find the 
anus. There are four vessels destined to convey the circu- 
lating fluid; a dorsal, an abdominal, and lateral vessels. 
These tubes carry red blood, and have a well marked 
systole and diastole. Eight pulsations occur in the course of 
a minute. I have frequently placed the H. vulgaris under 
the microscope, in order to discover a central organ of the 
vascular system, or what corresponds to the heart, but with- 
out effect. According to the opinion of some physiolo- 
gists, the several dilatations occurring in the course of the 
abdominal blood vessel, which, in the present instance, assume 
the figure of a diamond, (a portion of which is seen, mag- 
nified, in Fig. 5.) answer very effectually this purpose. 
The food of the H. vulgaris consists of the smaller kind of 
earth-worms, &c. which, in like manner with the H. san- 
guisuga , it swallows whole. 
In the summer of 1815, I kept several of these animals, in 
order to discover their mode of propagation. Examining 
the vessels that contained them, from time to time, I found 
them to be oviparous : the ova being enveloped in a gela- 
tinous mass, surrounded by a firm membrane, to which we 
attach the term of capsule. These ova. I preserved many 
months, but they proved unproductive. Disappointed in this 
my first attempt, I resolved to continue my research, and 
again collected during the last summer, a considerable 
number; when the object I had in view, was fully attained. 
