146 
Prof. Miall and Mr. N. Walker on the 
of food. Helophorus and some other aquatic Coleopterous 
larvae might also be quoted. 
A rather amusing application of capillary forces is 
witnessed if we bring a clean needle, half-immersed in 
water, near to the spiracular cup of a floating Pericoma 
larva. The cup is so strongly attracted that the body of 
the insect can be dragged about as if glued to the needle. 
This is the handiest way of submerging a larva. If two 
floating larvae are brought near one another, the bubbles 
cohere and run into one ; then the larvae are glued 
together, tail to tail, and cannot, so long as they float, 
disengage themselves. These are mere curiosities, and 
have nothing to do with the behaviour of the larva under 
natural conditions. What is practically important is that 
the larva, when it clings to the bottom, as it almost in- 
variably does, should be able to breathe uninterruptedly 
so long as the water is shallow; and if the depth is much 
increased, should be able to retain a bubble of sufficient 
size to support respiration until it can adapt itself to the 
change of level. 
Three types of larvae, probably belonging to as many 
distinct species, occur at Meanwood and Adel. That of 
P. canescens has relatively large anal processes. A second 
(undetermined) species has a larva of about the same size, 
with relatively small processes. In a third (undetermined) 
species the larva is only about half as long, while the anal 
processes are relatively intermediate in length. 
When the time of pupation is at hand, the larva quits 
the water. It either burrows into the bank or climbs 
upon a stone which rises well above the water, and there 
pupates. One favourite habitat of the larva, that is, the 
thick felted mass of algae covering earth or stones in very 
wet, but not submerged places, serves equally well for 
the pupa, and it often remains there until the fly emerges. 
The pupa of Pericoma is 3^ mm. long, and much 
resembles those of many other Tipulidae. It is provided 
with a pair of prothoracic respiratory trumpets, which are 
club-shaped, with a short stalk and a cylindrical terminal 
part, which is much longer and wider than the stalk. 
The stalk is transversely wrinkled. The surface of the 
rest of the trumpet is roughened by many small promin- 
ences. A large trachea traverses the organ, and opens 
by a double row of circular foramina, which extends along 
the rounded extremity of the trumpet and a little way 
down its inner side.* 
Cf. Jhcranota, Trans. Ent. Soc, 1893, pi. xiii., fig. 34. 
