284 



CRUSTACEANS. 



of the head and thorax are more or less reduced, being either absent or converted 

 into adhesive hoops or suckers. 



FISH-LICE. 



a, Lernceonema (enlarged 3 times) ; b, Brachiella (enlarged 9 times) ; c, Pennella (enlarged 5 times) ; 

 d, Hcemobaphes (nat. size) ; e, Caligus (enlarged 3 times). 



Order CLADOCERA. 



The members of this order take their names from the large and branched 

 antennae, which serve as swimming organs. They are all small, and the carapace 

 forms a bivalve shell enclosing the greater part of the body, this carapace being an 

 extension of the dorsal surface of the head-segments. An example of the order is 

 the water-flea (Daplmia pulex), to which Acanthocercus, represented in the 

 figure on p. 285, is nearly allied. Here the body is narrowed in front, and at 

 the posterior end, where the carapace (S) is deeply notched, is the tip of the 

 abdomen (C), bearing the pair of rigid barbed setae, from which the genus 



