24 
HYSANURA. 
while these latter have a suctorial mouth, that of the 
Bird-lice is formed for biting, consequently the true louse 
with its sharp retractile proboscis, will come under the 
Order Rhyncota, from which the other is excluded on 
account of the structure of its mouth; so difficult a 
matter it often is to form a classification that shall 
include and exclude all that is required. But not¬ 
withstanding the difference between the mouths of the 
true lice and the bird-lice, the general similarity of the 
whole structure of the animals will authorize us to place 
them both in the division of the Rhyncota. 
The Spring-tails ( Poduridce ) and Silver-scales {Lepis- 
midw ), first grouped together by Latreille under the 
name of Thysanura, from the fringed tails of some of 
the species, have lately been formed into two distinct 
orders by Sir John Lubbock, under the names of 
Collembola and Thysanura , in his valuable “ Mono¬ 
graph for the Piay Society.” They frequent dark places, 
but while the former, for the most part, prefer moist 
situations, and can endure great cold—I have seen 
numbers on ice under stones on the Swiss glaciers—the 
latter like dry walls and warm rooms. In the Collem- 
bola there is a remarkable organ underneath the ab¬ 
domen, called the ventral tube or sucker, whose function 
is to enable the creature to adhere to surfaces by the 
emission of some viscous fluid. From this Sir John 
Lubbock has proposed the name of the order." In most 
of the Collembola the tail, which is forked, is bent under 
the body, forming a jumping organ, by its sudden ex¬ 
tension ; in some species there is no saltatory organ. 
* 
From koWij “glue,” and t/t&Aoe “a peg.” 
