DIAPTOMUS. 221 



by five of different lengths. In the male, the right an- 

 tenna alone has the swelling and hinge-joint, which cha- 

 racterise the sex. This joint is formed in the same manner 

 as that in the Cyclopidae. 



'Hie antennnles (t. XXVI, f. 2 a) are of considerable size, 

 and bifid ; two branches of unequal length, arising from a 

 common footstalk. The shorter of the two can be moved 

 backwards or forwards at the pleasure of the animal, and 

 consists of six articulations, the first of which is stout, and 

 inserted into the common footstalk, and has four stout 

 setae springing from its edge. The second, third, fourth, 

 and fifth are very short, and each is furnished on its edge 

 with a stout seta ; while the last is of considerable length 

 and is provided at its extremity with three long setae. 

 The longer branch is composed of three joints. The first 

 is articulated with the body of the animal, and the third 

 terminates in several long filaments, which have a joint in 

 the middle of their length, adding much to their supple- 

 ness. These organs the little creature puts into rapid 

 action, and so causes a regular whirlpool in the water, 

 which attracts every object into its centre, and guides 

 them into its mouth. 



The labrum or lips consist of two small, somewhat 

 foliated-looking bodies, almost transparent, which, when 

 any object fit for food passes into the mouth, are seen to 

 separate from each other and open a passage for it. 



The mandibles (f. 2 5} resemble those of the Cyclops 

 (already described), but have the palpiform branch much 

 larger and bifid. 



The neck terminates in a horny acute point, under 

 which are six small teeth on the same plane. 



The foot-jaws are three pairs in number. The anterior 

 or first pair (f. 2 c, d] consists of a broad, heart-shaped 

 plate, with a smaller one of the same form attached to its 

 upper edge, both having numerous setae springing from 

 them, in the larger consisting of four on one side, and 

 eight on the other ; while a third, or smaller plate, bifid, 

 and equally beset with a number of hairs, springs from 



