312 
MR. WILSON ON THE STRUCTURE AND DEVELOPMENT OF 
the abdomen is long, it is frequently seen to present a succession of curves and to assume 
an undulated position. Besides flexion, the abdomen is capable of contraction both 
in the longitudinal and horizontal direction. I have sometimes seen one or two 
horizontal contractions which have straitened the diameter of the cylinder very con- 
siderably, and have given it the appearance of being tightly constricted by a string. 
The structure of the interior of the abdomen, like that of the thorax, is difficult to 
determine, on account of the extreme transparency of the animal and great number 
of adipose vesicles which, in clusters of various sizes, form the subcutaneous stratum. 
Externally to this stratum is a thin membrane which lines the epidermic case, and 
which, under compression, I have sometimes seen separated to a greater or less extent 
from the latter. The more general appearances of the abdominal contents are, — a 
large, rounded or oblong mass of a light brown colour, situated close to the thoracic 
extremity; another light brown mass at about one third from the extremity of the 
tail ; an irregular cellular mass between the two former, and a transparent portion at 
the caudal end. The most anterior of these masses is composed of nucleated gra- 
nules ; in one instance it presented a distinct pouch-like figure with well-defined 
boundaries, but more usually it is irregular in form, sometimes extending for a short 
distance into the thorax, and at other times being prolonged by a pointed process 
backwards. Whatever its form, it is traversed through the middle by a curved, cylin- 
drical canal, which appears to represent the stomach, the dark granules being very 
probably hepatic corpuscles. The cellular mass which succeeds the gastric organ 
consists of an assemblage of transparent vesicles of various magnitude, some large 
and some small. In the midst of these the alimentary canal may generally be traced 
as a slightly shaded band, somewhat curved in its course. The third mass, namely, 
that which occupies the commencement of the posterior third of the abdomen, is 
composed, like the first, of nucleated granules or cells: this mass is smaller than the 
first ; I have been unable to trace the alimentary canal through it, and I am inclined 
to regard the granules as constituting the ovarium. The remaining part of the abdo- 
men I have described as being transparent, and empty of granules ; this, however, is 
not constantly the case, for the granules sometimes extend to the very extremity of the 
abdomen. In a few instances I thought that I could perceive the latter part of the 
alimentary canal passing through this part of the animal and terminating by a dilated 
cloaca at the anal aperture. 
In the course of my observations on the Entozoon foUiculorum , I have distinguished 
two principal varieties of the adult animal which are marked by strongly character- 
istic, if not by specific features. The first of these is of large size, fine proportions, and 
is remarkable for the great length of its abdomen and the roundness of its caudal 
extremity. The second is characterized by a certain degree of clumsiness of form, 
shortness of abdomen, and pointedness of the caudal extremity. 
The long form varies in size from the to the 4V of an inch in length ; the 
latter measurement, that is, somewhat more than a quarter of a line, being that of the 
