210 CRUSTACEA. PAKT m. 



other lias not. The Apus cancriformis is an example of 

 the first. It is about two inches and a half long, and is 

 a large animal compared with the others of its class. Its 

 head and thorax are covered by an oval carapace, and 

 its cylindrical body is composed of thirty articulations. 

 It has a compound movable eye in the middle of its 

 forehead, and a sessile eye on each side of it. All the 

 members that follow the apparatus of the mouth have 

 a foliaceous form, and are in constant motion even 

 when the animal is at rest. The Apus has sixty pairs 

 of jointed legs ; the number of joints in these and in the 

 otner appendages is estimated to be not less than two 

 millions. However, the instruments chiefly used for 

 locomotion are the first pair of feet, which are very long 

 and serve for oars ; with these the animal can swim freely 

 in any position, but when they are at rest it floats on 

 the surface of the stagnant water in which it lives, and 

 the fin feet maintain a constant whirlpool in the water, 

 which brings the small animals on which it feeds to its 

 mouth. 



The Branchipes stagnalis, which may be taken as a 

 type of the second order, has a perfectly transparent 

 segmented body nearly an inch long, eleven pairs of 

 pale red gill-feet, antennse of bluish green, and a long 

 tail ending in red bristles. The head has two large 

 eyes on movable stems, and a sessile black oculus be- 

 tween them. Filiform antennse spring from the upper 

 part of the head ; the other pair, like two large horns, 

 are turned downwards. The last ring of the swimming 

 tail has two plates with ciliated appendages. 



The Artemia salina differs very little from the Bran- 

 chipes. It abounds so much in the brine pans at 

 Lymington and other salt works, as to give a red 

 tinge to the nearly concentrated brine, the temperature 

 of which is so high that no other animal could live for 

 a moment in it. 



