APODIDiE. 
25 
setae which beset it in the preceding, there are only a few 
(about twelve) longer tubular and plumose setae. They 
differ, however, still further in this particular, that in this 
pair we observe, between the hinder portion of the 
branchial plate and the external claw, another plate make 
its appearance, of an ovoid shape, and edged with short 
setae. These feet are called by Schoeffer the lamellar 
branchial feet. As they succeed each other, we see the 
external claw become gradually more round-shaped, and 
the branchial plate lose, more and more, its triangular 
form, till it becomes quite oblong, while the organs them- 
selves become so small, that they are at last only rudi- 
mentary. 
The tail consists of one segment, larger and flatter 
than any of the immediately preceding ones of the ab- 
domen, which are nearly cylindrical. It is marked by 
three short, blunt projections at its extremity, and gives 
off two very long, round appendages, each consisting of 
an immense number of small articulations ; Schoeffer 
counted them, and found each to consist of 480 joints. 
As the animal can give a degree of motion to these ap- 
pendages, they may be useful as a sort of rudder, to guide 
its movements through the water. In the centre of this 
caudal segment, between these two long appendages, is 
situate the anus. 
The number of articulations, or separate pieces, of 
which the body of these animals is composed, is extraor- 
dinary. Schoeffer, with wonderful patience, undertook 
the task of counting them, and in a table, in which he 
enumerates them seriatim, reckons the number to be 
1,802,604 ! and Latreille says that we may safely take 
them to be not less than two millions ! ! 
The Apus inhabits stagnant waters, though they are by 
no means so commonly to be met with as many of the 
other kinds of Entomostraca. They appear to be more 
local, and sometimes disappear from their usual haunts, 
reappearing some years afterwards in the very same place. 
“ In warm, calm weather,” says Schoeffer, “ they assemble 
