272 The X.Z. Journal of Science and Technology. [Jan. 
larvae of the caddis-flies of the family Leptoceridae, which form their cases 
of the green weed Nitella. The stomachs of a number o'f trout were found 
to be filled with this green weed, which on being placed in a basin of water 
was seen to consist entirely of caddis-fly cases, many of the larvae being 
still alive within the trout’s stomach. Another important food was a small 
mollusc, Potamopyrgus sp., of which no less than 140 were counted in the 
stomach of a “ slab ” taken at Rotorua. Other foods found less commonly 
were the larvae of dragon-flies, may-flies, stone-flies and the other families 
of caddis-flies, occasional remains of the crayfish, small fish, and a number 
of insects of various kinds which may be considered to have no definite 
value as trout-food, being only chance captures. 
Besides these, it is important to note that some trout-stomachs were 
found containing nothing but pebbles, and several were quite empty. 
A considerable number of the trout examined were definitely “ slabs.” 
The slabby condition appeared to be due not only to the usual poor health 
of the fish for some months after spawning had taken place, but more 
definitely to both semi-starvation and indigestion. It was not surprising 
to find that fish with their stomachs empty, or filled with pebbles only, 
were in poor condition. But there were also cases in which the slabby 
condition appeared to have been caused by the indigestibility of the food. 
In one case the large claws of a crayfish were found fixed inside the 
stomach of a trout in such a way as to block the passage of other food ; 
and they had evidently been there a considerable time, seeing that all the 
rest of the animal had been completely digested. This led me to conclude 
that the crayfish is only a good food for trout when it is of not too large a 
size. Consequently the introduction of any larger or more vigorous species 
of crayfish than the one endemic in the region ought not to be encouraged. 
(ii.) The Neuropteroid Fauna of the Streams and Lakes. 
The neuropteroid insects inhabiting the streams and lakes of the Hot 
Springs region may be divided into six orders, three of which belong to the 
more primitive division of the winged insects—viz., those that have no 
true pupa or resting stage (Hemimetabola), and three belong to the more 
highly evolved division, possessing a true pupal stage (Holometabola). 
They may be classified as follows :— 
Division Hemimetabola (winged insects without a true pupal or 
resting stage). 
Order 1. Perlaria, or stone-flies. 
Order 2. Plectoptera, or may-flies. 
Order 3. Odonata, or dragon-flies. 
Division Holometabola (winged insects possessing a true pupal 
stage). 
Order 4. Megaloptera, or alder-flies. 
Order 5. Planipennia, or lacewings. 
Order 6. Trichoptera, or caddis-flies. 
(Note. —The scorpion-flies, order Mecoptera, are not represented in 
the region under discussion.) 
Of the six orders enumerated we may omit from the discussion Order 5 
(lacewings), whose larvae are either terrestrial or else lurkers along the moist 
borders of streams. They attack the larvae of the other orders which are 
of value as food for trout. Thus, in so far as they affect the problem at all, 
they act detrimentally to the food-supply. But they are exceedingly rare 
