0. L. Boulenger 
143 
of the second stage. The general shape of the larvae is therefore 
determined by this outer skin, and in describing and measuring them it 
is necessary to distinguish carefully between this sheath and the enclosed 
larva which almost completely fills it. 
The total length of the free larvae, including the tail, varies from 
•85 to 1-15 mm., the average length being about 1 mm. The body has 
a maximum breadth of 25-30p and is approximately cylindrical, tapering 
however anteriorly and posteriorly but only moderately towards the 
cephalic extremity which terminates in a rounded head about 15p in 
width. Posteriorly the body passes gradually into the very slender 
tail which has a length of about one-thircl of the total length of the 
Fig. 1. Tail of larva with fork-like malformation of posterior end. x 750. 
larva. In many of the larvae a slight constriction is to be seen a short 
distance behind the commencement of the tail, the posterior portion of 
which is often difficult to see except under high magnifications, having 
a thickness of little more than lp. 
Abnormalities of the caudal region were frequently observed, the 
commonest being a fork-like malformation of the extremity, as shown 
in Text-fig. 1. 
The skin or “shea th ” is comparatively thick and provided with closely 
set transverse striae, oidy visible under high powers of the microscope; 
it is completely closed, the position of the mouth is however indicated by 
a slight thickening at the anterior extremity. 
