144 
Nematodirus filicollis Rucl. 
Under normal conditions and when uncontracted the enclosed 
larva completely fills the ensheathing skin with the exception of the 
slender tail, for this reason the sheath is sometimes inconspicuous, it 
can however be readily observed when the body is flexed, being thrown 
into distinct and regular folds on the concave surface; the larva has 
moreover considerable powers of contraction and when contracted the 
outer skin can be seen projecting at each extremity. 
As mentioned above the enclosed larvae do not project into the 
tail-regions of the sheaths, they are therefore considerably shorter than 
the latter, measuring 5-3-7 mm. in length. 
The shape of the head differs somewhat from that of the cephalic 
extremity of the sheath, being slightly truncated anteriorly, not rounded. 
There are no distinct lips, cephalic papillae are however present, in the 
form of six small but highly refractive spots. 
The tiny mouth leads into a short buccal cavity. The oesophagus 
is slender, 180-220/z in length, it increases in breadth posteriorly but 
does not terminate in an oesophageal bulb and is not provided with a 
“dental ” apparatus. The intestine is also narrow and consists of eight 
cells only, four dorsal and four ventral alternating with one another; 
these intestinal cells are rather dark in colour and usually filled with 
reserve granules and vacuoles which conceal the nuclei, the latter are 
however occasionally visible. From the termination of the intestine 
a very slender rectum leads to the anus, a tiny opening situated 
on the ventral surface about 50/x from the posterior extremity of the 
larva. 
The tail of the larva is peculiar and extremely characteristic, differing 
markedly in shape from that of the sheath; it is divided at the posterior 
extremity into dorsal and ventral lobes in such a way as to appear deeply 
forked when seen in a lateral view. The two lobes vary somewhat in 
shape and size in different individuals, the dorsal is however usually 
somewhat larger than the ventral which it conceals in a dorsal view 
(Text-fig. 2). Between the dorsal and ventral lobes is an elongated 
rod-shaped process recalling the tail-spike of the adult Nematodirus 
female, it has a length of about 13 /x and projects well beyond the lobes 
of the tail. 
The excretory apparatus is difficult to make out in the ensheathed 
larva, the terminal canal can however be seen in the majority of 
individuals leading to the minute excretory pore, which opens on the 
ventral surface a little anterior to the junction of intestine and oeso¬ 
phagus and about 150 /a from the anterior extremity of the body. 
