SOME DIFFICULTIES IN THE LIFE OF AQUATIC INSECTS. 353 
should be stored and economically used, which contain no haemoglobin 
in their blood. Hence, while we have a tolerably satisfactory reason 
for the occurrence of hemoglobin in a number of animals whose respi- 
ratory surface is limited, and whose surroundings make it a matter of 
difficulty to procure a sufficient supply of oxygen, we have to admit 
that many similar animals under the same conditions manage perfectly 
well without hemoglobin. Such admission is not a logical refutation 
of the explanation. I might fairly put forward the baldness of man- 
kind as at least the principal reason for wearing wigs, and this expla- 
nation would not be impaired by any number of cases of bald men who 
do not wear wigs. The fact is that the respiratory needs (even of 
closely allied animals) vary greatly, and further, there are more ways 
than one of acquiring and storing up oxygen in their bodies. 
Hither the storage capacity for oxygen of the Chironomus larva is 
considerable, or it must be used very carefully, for the animal can sub- 
sist long without a fresh supply. I took a flask of distilled water, 
boiled it for three-quarters of an hour, closed it tight with an India- 
rubber bung, and left it to cool. Then six larve were introduced, the 
small space above the water being at the same time filled up with car- 
bonie acid. The bung was replaced and the larvee was watched from 
day to day. Four of the larve survived for forty-eight hours, and one 
till the fifth day. Two of them changed to.pupze. Nevertheless, the 
water was from the first exhausted of oxygen, or nearly so. 
The Chironomus larva is provided with implements suited to its mode 
of life. The head, which is extremely small and hard, carries a pair of 
stout jaws, besides a most complicated array of hooks, some fixed, some 
movable. The use of these minute appendages can not always be 
assigned, but some of them are apparently employed to guide the silky 
threads which issue from the salivary glands. The first segment behind 
the head carries a pair of stumpy legs, which are set with many hooks. 
These are mainly used in progression, and help the larva to hitch itself 
to and fro in its burrow. A similar, but longer pair of hooked feet, is 
found at the end of the body. This hinder pair serves to attach the 
animal to its burrow when it stretches forth in search of food. 
Creeping aquatic larvie, such as Ephydra, possess several pairs of 
legs in front of the last pair, but the burrowing species, such as caddis- 
worms, agree with Chironomus, not only in their mode of life, but also 
in the reduction of the abdominal legs to a single pair, which are con- 
spicuously hooked. 
The larval head in this, as in many other aquatic insects, is far 
smaller and simpler than that of the fly. The larval head is little more 
than an implement for biting and spinning, by no means such a seat 
of intelligence as it isin higher animals. In Chironomus it contains no 
brain; the eyes are mere specks of pigment, and the antennwe are 
insignificant. But the head of the fly incloses the brain, and bears 
elaborate organs of special sense—many-facetted eyes, and in the male 
H. Mis. 334, pt. 1——23 
