CADDIS-^OEMS AND THEIE METAMOEPHOSES. 
291 
as some other species, which spin silken threads, are destitute 
of this organ, it is hardly likely that this organ has the function 
attributed to it by Eeaumur. The fleshy abdomen consists of 
nine segments, upon the first of which there are three conical 
tubercles, two lateral and one medial ; at the end of the last 
segment, which is smaller than the others, there are two mov- 
able appendages of variable form ; in the true PhryganecB these 
appendages are small hooks, by means of which the animals 
attach themselves firmly to their cases. In the case of those 
larvae which reside in immovable houses, these anal hooks are 
elongated and placed upon long footstalks. Numerous filaments, 
of various forms, beset the abdominal segments of these larv^ ; 
sometimes they are arranged in tufts, sometimes they are 
isolated. A microscopic examination soon reveals the function 
of these membranous filaments ; they are organs of respiration. 
Some species are destitute of external gills, the respiration 
being efiected by spiracles on each side of the abdominal seg- 
ments. Let us look at the internal organs of a caddis-worm. 
We will select a specimen of Pliryganea fusca iov examination : 
this is a common species, and builds a house of small stones, 
or sand, to which are attached, longitudinally, long pieces of 
twigs, rush, or grass, &c. ; being of large size, the anatomy is 
easily made out. We remove the larva out of his house by 
making, with the point of a fine pair of scissors, a slit all the 
way from the one extremity to the other, and then fold back 
the margins ; next we give the caddis a dose of chloroform to 
smell, and then pin him down on our dissecting trough, one pin 
being fixed through the thorax, the other through the anal ex- 
tremity : on making a cut from one end to the other, and 
pinning back the sides, we notice a long thick black tubular 
body, which is a portion of the intestinal track coloured by 
food; a little care will enable us to disentangle it from the 
surrounding viscera, with a view to a detailed examination. 
The alimentary canal is a long straight tube, without any cir- 
cumvolutions, passing from the mouth to the anus. M. Pictet 
draws attention to the absence of circumvolutions, as being 
remarkable in an animal whose food is solely of a vegetable 
nature; he considers that the shortness of the tube is amply 
compensated by its diameter, which is considerable. It is quite 
certain, however, that the larvae of Phvyganece are not exclu- 
sively vegetable feeders. I have known them devour worms, 
and the larvae of other insects, and Miss Smee fed her specimens 
on pieces of “uncooked meat, which they would eagerly seize, 
and ravenously devour.” I am also able to confirm the same 
lady’s statement that these larvae devour the mollusc Dreissena 
joolymorpha. The intestinal track consists of oesophagus, crop, 
stomach, the small and large intestines, and the coecal ap- 
