WATER-FLEAS. 



531 



mentioned, Europeans turn from insects, etc., with disgust, -wliile eating 

 crabs and shrimps without hesitation. Food is more a matter of fashion 

 than of anything else, after all. 



A most ingenious theory has lately been propounded by Mr. H. M. 

 Bernard, in his work on the Apodirhe. He considers the Ch-ustacea to have 

 originated from the Amielida, and that the earliest Crustacea were simply 

 Annelida with the head bent down under the body ; but this is a matter on 

 which only specialists are entitled to express an opinion. Nevertheless, we 

 may begin the Crustacea with the Entomostraca, as the grovip nearest ap- 

 proaching to the Annelida. We may add that the Pycnogonida, which we 

 have included with the AracJmida, have been placed by some authors in the 

 Crustacea, while others have regarded them as forming a distinct class of 

 Arthropoda by themselves. 



SUB-CLASS I.— ENTOMOSTRACA. 



This large section is only retained as a matter of convenience to include the 

 smaller Crustacea, many of which exhibit forms which have little resemblance 

 to the more typical Crustacea. It includes most of the parasitic species. The 

 Cirripedia are sometimes treated as an additional order of Entomosto-aca. 



Oedee I. — Phyllopoda. 



The Phyllopoda have received their name from their leaf-like swimming 

 legs, of which there are four pairs, or more. Sometimes more or less of the 

 animal is covered by a bivalve shell, somewhat as in the Ostracoda, or by a 



Jiff. 2.— Water-Flea 



(Daphnia pulex). 



Magnified. 



Fiff. 3. — Apus cancri- 

 /urmis. Nat. size. 



Fig. i.—HuTN-E 



Shrimp 



(Ai'femia salincCj. 



MaguiHed. 



solid carapace ; in other cases this is wanting. Some are marine, while others 

 inhabit fresh water. They have usually two eyes, which, however, are some- 

 times contiguous. Three families of this order may be briefly noticed. The 



