NO. 7 A NEW COPEPOD HABITAT ^WILSON 7 



restricted that the demand for some sort of guidance is greatly en- 

 hanced and becomes imperative. This demand is met by a greatly in- 

 creased tactile sensibility in the first antennae, which here become 

 " feelers " in the fullest sense of the term. The normal copepod usu- 



FiG. 3. — a, first antenna of a male Arcnosctclla spinicatida, with 

 two large aesthetasks ; b, first antenna of a male Nitocra chclifer, 

 with a single long and stout aesthetask ; c, first antenna of a male 

 Enicrtoiiia gracilis, with a single enlarged aesthetask. 



Fig. 4. — First antenna of Arenocalanus tuiiiidtis, female, a new 

 genus of sand-dwelling calanids, showing an exceptional increase 

 in the number of aesthetasks. 



ally carries a single sensory club or aesthetask on each of the first 

 antennae. In these terraqueous copepods the size and length of the 

 aesthetasks may be considerably increased, as happens more often 

 in the males (fig. 3). In the females either the number of aesthetasks 

 is multiplied as in figure 4, or they are supplemented by thick finger- 



