ENTOMOSTRACA. 127 



CHAPTER XL 



ARTICULATA (ARTIc'lJLUS, A JOINT). 



THE animals belonging to this subkingdom are spe- 

 cially distinguished by the body and limbs being 

 jointed : as familiar instances, may be mentioned the 

 lobster, the wood-louse, spiders, insects, and worms. 



Taking the class Crustacea, to which the two first 

 animals belong, we find interesting microscopic forms 

 in the subclass Entomos'traca (evrofiov, insect ; ocrT/ao- 

 KOV, shell). 



ENTOMOSTRACA. The animals contained in this 

 Order are met with in every pool or pond, some of 

 them inhabiting the sea. They are mostly minute, 

 yet visible to the naked eye, forming specks swimming 

 actively or leaping through the water ; hence some 

 of them have been called water-fleas. The body of 

 the animal is protected by a shell or car'apace, which 

 in some consists of a single piece (PL IX. fig. 30), 

 while in others it consists of two similar parts or 

 valves (fig. 31), in the latter case the joints of the 

 body being indistinctly visible. The head is furnished 

 with usually two projecting feelers or antennae (an- 

 ten'na, a sail-yard), one of which is uppermost or su- 

 perior (PL IX. figs. 30, 31, 34 a], the other lowermost 

 or inferior (figs. 30 and 34 b) ; and these are often 

 used for swimming. The antennae are jointed, and 

 sometimes beautifully plumose (pluma, a feather) or 

 feathery, i. e. furnished with rows of long and very 

 slender filaments. There are several pairs of jointed 

 legs, some of which serve as jaws (foot-jaws), while 

 others are finely filamentous to serve for swimming 



