PHYLLOPODA 



425 



ORDER VII. 



LEAF-LEGGED CRUSTACEA (PHYLLO- 

 PODA). 



In this group, of which Water Fleas 

 (Daphnia) may be taken as familiar 

 examples, the body is enclosed within 

 a saddle - shaped shell. They are, 

 however, easily distinguished from 

 the Ostracoda by the two large arm- 

 like organs (second pair of antennae) 

 developed on their head, by the help 

 of which they move in jerks through 

 the water. Most of these delicate 

 creatures are of glassy transparency, 

 so that not only all their internal 

 organs and the cavity in which the 

 larvse are developed, but also the 

 beat of the heart and the circulation 

 of the blood, may be observed from 

 without. These creatures are placed 

 in the order Phyllopoda on account of 

 their foliaceous (gill-bearing) feet. 



To the same order also belongs 

 the interesting genus Apus. This 

 animal measures about 1£ inches in 

 length, and carries a large dorsal 

 carapace and a large number of pairs 

 of feet, which are kept in constant 

 vibratory motion. It is found only 

 in spring in standing pieces of water 

 which had previously completely dried 

 up, for, strange to say, its eggs re- 

 quire to have lain dry for a time 

 before they can be hatched. 



ORDER VIII. : 

 BARNACLES (CIRRIPEDIA). 



To objects floating on the sea we often 

 find permanently fixed elegant-looking 

 organisms, borne upon movable stalks, 

 and, like mussels, enclosed within hard 

 shells. From their external resem- 

 blance to molluscs, they were accord- 



A Wateb Flea (Daphnia zschokkei) lying 

 on its Right Side. (Magnified about 

 thirty times. ) 



l.S. andr.S., Left and right halves of the 

 saddle-shaped shell, terminating in the 

 spine (St.) ; of the right half of the shell 

 only a small portion is visible ; between 

 the two halves some of the spines of the 

 abdomen (HI.) are seen protruding; F.l. 

 and F.2., first and second pairs of an- 

 tenme ; B. , foliaceous feet ; A. , compound 

 eye (with five lenses) ; N. , portions of the 

 nervous system (nerve ganglia) ; D., in- 

 testine, terminating in Af. , the anus ; 

 H., heart ; K., ovary, from which several 

 freshly developed ova (E.) are entering the 

 "brood pouch" (B.), which is closed 

 behind by three folds (Fa. ). 



