214 Transactions.— Zoology! 



prevented from actually leaving the case by his abdomen, which 

 is too large to be withdrawn from either end. The head and 

 thorax of the larva are very strong in comparison with those 

 portions permanently retained inside, the legs being constructed 

 to fold up into the smallest possible compass, a cavity existing 

 in each joint for the preceding one, this being a structure which 

 is almost universal among the caddis worms. The two organs 

 situated on the posterior segments are doubtless respiratory in 

 their function, a large air-tube taking its rise from each, and 

 rarnifving through the bodv in all directions. 



When alarmed, these insects retreat into their cases with 

 lightning rapidity, remaining concealed until the danger is 

 passed. Their food probably consists of the green weed, 

 although they are perhaps carnivorous, feeding on the rotifers and 

 other animalcula?, which swarm in the water where they are found. 



With regard to the method employed by the young larva in 

 constructing, and subsequently enlarging, his case, I can give no 

 positive information, although it is undoubtedly made of a vis- 

 cous fluid secreted by the insect, which hardens when exposed 

 to the water ; this secretion is no doubt analogous to the silk of 

 caterpillars, which always exists in the form of a gummy fluid 

 before being spun. In a few Lepidopterous larva 1 (Centra, etc.) 

 it is employed as such to construct the cocoon, which is con- 

 sequently of a much stronger consistence tban where the ordi- 

 nary silk is used. When about to change, the insect fixes his 

 case down by four ligaments, two at each end, the extremities 

 of these being firmly fastened on to a stone ; he then closes the 

 small aperture, and constructs a curious arch-shaped partition 

 of dense material inside, a short distance from the broad end 

 (fig. 2). In about a week's time he is transformed into a pupa, 

 having the limbs, etc., free from the body, but incapable of 

 motion. The fixing down of the case prior to the change may 

 be easily performed by the larva from each of the apertures, 

 which are no doubt left open till the last for this purpose. Be- 

 fore the final transformation the pupa breaks through the 

 partition at the broad end of the case, and wriggles to the sur- 

 face, the imago ascending a blade of grass to dry and expand its 

 wings. The little exuvia of the pupa may be often noticed 

 floating on the water, and the empty cases are very conspicuous 

 on the sides of a glass aquarium, where the insects generally 

 fix them down when in captivity. 



This Caddis Fly (fig. 3) must be tolerably common during 

 the summer, but owing to its small size would not be likely to 

 attract attention. I have never observed it in a state of nature, 

 all my specimens having been reared from the larva. It is 

 probably uudescribed ; but as there are no catalogues of these 

 insects at present published, it is impossible to speak with 

 certainty on this point. 



