142 



LEAVES FROM MY NOTE-BOOK. 



But by suddenly lifting out of the water a leaf with many larvae 

 upon it, one may get proof of the spinning of fresh threads. One 

 or two are pretty sure to let go and drop a foot or more in the air, 

 and the thread can be seen to glisten in the sun, and to lengthen 

 itself at the pleasure of the insect. The Simulium larva, gifted 

 with this power of instantaneously manufacturing a rope, can 

 hardly be taken at a disadvantage." 



The salivary glands which secrete the silk are unusually large 

 in this larva ; they extend the whole length of the body, and then 

 bend forwards for a third of its length. But the next question is 

 as to how the safety of the pupa of Simulium is provided for ; it 

 seems that such an inactive, defenceless body must immediately 

 be carried away to destruction by a rushing stream. The pupa is 

 however as safe as the larva, being protected in a kind of nest, 

 glued, somewhat like the nests of some swallows, to the stem of a 



Fig. 6. — A^ Four pupte of Shnulium in their cocoons attached to aquatic 

 stem. B, Pupa of Simulium^ removed from its cocoon. 



water weed (Fig. 6). When the little nest is first formed it is 

 completely closed ; but when the insect has cast its larval skin, it 

 knocks off one end of the cocoon, and thrusts the fore-part of its 

 body into the current of water, whilst the hinder part is firmly 



