APODIDyE. 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 Schceffer 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 ; Schceffer 

 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. Schceffer, 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, cairn weather," says Schceffer, " they assemble 



