60 NEW ZEALAND NEUB.OPTERA. 



has not yet been recorded. The duration of life in this, 

 stage is usually considerable, extending over several 

 months. In New Zealand all the species seem to pass 

 the winter as larvae, completing their metamorphosis- 

 during the following spring or summer ; and as one 

 generation each year appears to be the rule, it is evident 

 that the larval condition, in such cases, lasts from seven 

 to ten months. During" this stage the insects are chiefly 

 vegetable feeders, some being said to feed on minute 

 alga? ; animal diet is not, however, entirely avoided, 

 and it is said by Pictet that not only do some of the 

 Phryganeida? eat other insects, but that they also some- 

 times devour their companions. 



At the end of the larval period of existence, the 

 creature closes its case by a light web spun at each end, 

 taking care not to prevent the ingress and egress of the 

 water ; it sometimes adds a stone or piece of stick, and 

 having thus protected itself changes to a pupa. During 

 the first part of this metamorphosis the creature is 

 completely helpless, for there is so great a difference 

 between the external structures of the larva and the pupa, 

 as to make the latter a new being, so far as these organs 

 are concerned. The changes take place in the interior of 

 the larval skin, and as they are completed, this latter -is 

 shed piecemeal. The resulting pupa greatly resembles- 

 the perfect insect, differing consequently very much from 

 the larva. The head of the pupa is armed in front with 

 two curious projections that are, in fact, enormously 

 developed mandibles ; they serve as cutting implements 

 to enable the pupa to effect its escape from its prison ; 

 they are cast off with the pupa skin, the perfect insect 

 being thus destitute of these organs. The abdomen of 

 the pupa differs from that of the perfect insect in 

 possessing external respiratory filaments ; the pupa? of 

 some species have also the middle legs provided with 

 swimming hairs, which do not exist in the imago. The 

 skin of the pupa is at first very soft, but it soon hardens, 

 and when about fifteen or twenty days have elapsed, the 

 pupa opens its case by means of the mandibular processes, 

 and swims through the water for some hours with its- 

 back downwards, finally ascending to the air by the help 

 of some solid object ; the pupa skin then swells and 

 splits, and the thorax of the imago protrudes ; this is 

 soon followed by the disengagement of the head and other 

 parts; and the imago, having thus escaped, the pupa skin 

 remains, floating on the surface of the water, a complete 



