605 
of the anterior part of the body, + I50 u in the middle of the 
body. So in the front part they are much thicker than more back- 
ward at the level of the middle part of the body. Later on this 
difference disappears: the straight truncated anterior extremity (fig. 3) 
of the almost cylindrical body is then even somewhat thinner than 
the middle part of the body, which has the appearance of the broken 
point of a pin. The posterior part of the body is tapered, represent- 
ing a sharp cuticular point in the male as well as in the female. 
In the male specimens of two different catches, in which a large 
number of larval, moulting and adult Oryuris occurs, this point bas 
a different length. In the one catch (No. 37) it is 230—300 u long, 
in the other (No. 42) 320—340 u. In these catches the length of 
the cuticular point of female larvae differs still more, however. In 
catch No. 37 it amounts to 140 —160 u, in catch No. 42 to 200—250 u. 
These differences in measurements we have also found in the 
length of the moulting male and female specimens. The male moult- 
ing larvae of catch No. 37 are 7.5—8 mm. long, those of No. 42 
only 5.6—6.4 mm. The lengths of the female moulting specimens 
are 10.25—I1 mm. and 7.5—9 mm. respectively. The adult speci- 
mens of these catches belong in the first case to the mastigodes-, 
in the second to the curvula-type. Perhaps the measurements stated 
support the opinion that Oxyuris equi (curvula) and Oxyuris masti- 
godes are independent species. 
As Rainier and Henry have remarked already, the male and the 
female larvae are distinguished by the difference in shape of the 
posterior end of the body. The distance of the anal opening from 
the posterior extremity (the cuticular point included) is much longer 
in the 9 than in the &. Figs. 1 and 2 explain this. The part of the 
body, situated between the anal opening and the cuticular point 
decreases strongly in thickness in the male, gradually in the female. 
The shape of the cuticular point is the same, but in the ¢ this point 
is somewhat longer than in the Q. For the measurements to compare 
the following table (see page 606). 
From this table it follows that the ratio between the lengths of 
the part of body situated between the anterior extremity and the 
anal opening and of that part situated between anal opening and 
cuticular point remains about the same during the growth of“ the 
larva and that in the ¢¢ it is almost half of that in the 22. 
The cuticular rings of the larvae differ in breadth. In the anterior 
part of the body they are broader than in the posterior part. 
In the smallest larvae the breadth amounts to about 16—28 u, 
in the largest larvae, just before the moulting stage, to + 60 u 
39 
Proceedings Royal Acad. Amsterdam. Vol. XXII. 
