HABITATION OP CADDICE-WORM. 



>33 



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- Fig 2 73.-C, PHRYGANF.A OR CADDICE-FLY 

 phosis into the Pupa State ; A, tube formed by its larva ; B, network at 



and a short time before its the entrance of the tube - 



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 Necrophorus (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 



