HABITATION OF CADDICE-WORM. 
533 
C, Phryganea or Caddice-Fly 
A, tube formed by its larva ; B, network at 
the entrance of the tube. 
so as to make a tube (a), in which the animal creeps along 
the bottom and sides of the brook it inhabits, and sometimes 
rows itself on the surface 
of the water. When full- 
grown, the larva attaches 
its case by threads to some 
large stone ; and then 
covers its mouth with an 
open net-work of threads 
(b), sufficiently close to 
prevent the entrance of 
insects, but with meshes 
permitting the water to 
pass through. In this way 
it undergoes its metamor¬ 
phosis into the Pupa state; 
and a short time before its 
last change it cuts the threads of the network, by means 
of two hooks with which its head is furnished, and creeps 
out of the water; soon after which it changes into the perfect 
insect. 
702. It is scarcely possible to point to any actions better 
fitted to give an idea of the nature of Instinct, than those 
which are performed by various Insects when they deposit 
their eggs. These animals never behold their progeny, and 
cannot acquire any notion from experience, therefore, of that 
which their eggs will produce; nevertheless they have the 
remarkable habit of placing, in the neighbourhood of each of 
these bodies, a supply of aliment fitted for the nourishment 
of the larva that is to proceed from it; and this they do, 
even when they are themselves living on food of an entirely 
different nature, such as would not be adapted for the larva. 
They cannot be guided in such actions by anything like 
reason, since the data on which alone they could reason 
correctly are wanting to them; so that they would be led to 
conclusions altogether erroneous, if they were not prompted 
by an unerring instinct to adopt the means best adapted for 
the attainment of the required end. 
703. Of this kind of instinct, the JSTecrophorus (fig. 274), a 
kind of Beetle not uncommon in our fields, offers a good 
example. When the female is about to lay her eggs, she 
