S. Yokogawa 
145 
The shape of the posterior ends of the larvae early in the second stage 
begins to show the sexual differentiation which becomes so prominent 
later. 
Colour. The cuticula of the larvae in the first parasitic stage is colourless 
while that of the adult worm is pinkish. The cuticula of the larvae in the 
second parasitic stage has a slightly yellowish tinge. They appear, however, 
at this stage as black or dark-brown spots or as curved strings on the mucous 
membrane of the intestine of the host, since the dense pigment of the intestinal 
cells shows through and gives its colour to the whole worm when examined 
with the naked eye. After completion of the third ecdysis, the colour of the 
cuticula not only increases in intensity but takes on the pinkish shade. As 
noted above the cuticula consists at this stage of two separate layers. These 
layers, the outer one of which probably represents an incomplete moult, have 
the same colour. The outer cuticula is much wider than the inner. The cuticula 
appears to have a yellowish-red colour when seen with transmitted light under 
the microscope, while it has a reddish or pinkish appearance by reflected light. 
(b) The Cuticula. 
The cuticula of the larva in the first parasitic stage does not differ from 
that of the mature free-living larva. It consists of a thin transparent membrane 
with closely set striations. When the larvae reach the next stage, the anterior 
part of the cuticle inflates and makes a peculiar cephalic area, the cuticular 
expansion. This cuticular expansion or the cephalic area consists of very thin 
cuticula without any striations. The other regions of the cuticula are relatively 
thick and have the transverse striations except the posterior inflation of the 
male which later forms the bursa. In this inflated bursal region the cuticula 
becomes thinner and thinner as the expansion increases. 
After the completion of the third ecdysis, the cuticula shows prominent 
longitudinal markings in the form of ten ridges. These longitudinal ridges 
begin a little behind the cephalic area and run parallel to the posterior end. 
At this stage, the transverse striations are not continuous around the cuticula 
but are found only on the longitudinal ridges. During this stage, the cuticula 
becomes looser and looser and a new cuticula similar to that produced in 
moulting develops under the old. The old cuticula finally separates from the 
new and a relatively wide space develops between them. Especially at the 
posterior end of the female, the outer cuticula is widely separated from the 
inner and forms a peculiar sac surrounding the anus and the vulva. 
The inner newly-formed cuticula has only transverse striations and not 
the longitudinal ridges which are so prominent on the outer cuticula. These 
two layers of cuticula are fused at the anterior tip, at the posterior limit of 
the cephalic inflation, at the anus and vulva of the female and over the whole 
of the bursa of the male. At all other parts of the body they are widely 
separated. 
Parasitology xiv 
10 
