THE INTERMEDIARY HOST OF FILARIA CYPSELI 
45 
Stage IV. (Fig. 7). — The parasite still increases in length, the width of the body 
remaining stationary. The anterior and posterior ends instead of being similarly 
bluntly rounded off show some differentiation. The anterior extremity of the para- 
site has become bluntly cone shaped, similar to the adult parent worm. The posterior 
is rounded and slightly flattened at its extremity, it has now lost its tubercle. The 
fine sheath enclosing the embryo is now more marked, there is a distinct space 
between it and the body of the worm, at the posterior end it forms a tag-like process 
which represents the covering of the posterior tubercle. The worm has now lost its 
markedly striated appearance. In the interior of the worm the alimentary canal is 
now seen differentiated off into pharynx and oesophagus, ending at a bulb-like thick- 
ening and intestinal tract. It does not occupy the whole width of the body cavity 
as in the last stage, and is seen to be moveable from side to side in the fresh state. 
The other structures mentioned in the previous stage are still more plainly seen. If 
the worm is dissected out from the fat body — now an easy matter, as the parasite 
generally becomes free in the process of dissection of the abdomen of the louse — 
active contractile movements of the parasite are seen. 
The following measurements were taken of one parasite in this stage directly 
after movements had slowed down in two per cent, formal in saline solution : — 
Total length 
Length to 
Length to 
Central width 
Width at 
Width at anus 
genital papilla 
genital papilla 
3 26 a 
7172 fx 
312-96 fjL 
2 9"3+ M 
26-08 a 
22-S2 M 
The pharynx and oesophagus up to the bulk-like thickening measured in this 
worm 162 fx. In this and the next stage of metamorphosis of the parasite, I believe 
it possible to distinguish the future male and female adult filaria. Thus the future 
male parasites may be distinguished as follows : The anal opening is situated at a 
greater distance from the posterior extremity of the parasite, and the end prominence 
is more marked ; behind it there is a marked constriction in the body of the parasite. 
When placed in normal saline solution the tail end tends to curl in. There is no 
genital papilla near the head representing the future vaginal opening. The parasite 
is smaller than those which have a genital papilla. 
Stage V (Fig. 8). — In this, the last stage so far seen in the development of 
the filaria, the worm is found free in the body-cavity of the louse ; it shows actively 
progressive and lively movements when placed in normal saline solution. In shape 
it is exactly like the adult parent worms, except that there is a slight constriction at 
the tail end, and the position of the anus is not quite subterminal. 
Contrasting it with the previous stage, the parasite shows a further increase in 
u 
