DAPHNIA 57 



phyllopod), in which we can recognize the basal protopodite 

 and two broad terminal pieces, the endopodite and exopodite. 

 The short abdomen articulates with the thorax and is bent 

 beneath it, where it may be seen often moving rapidly back 

 and forth. 



Exercise l. Draw an outline of a side view of the animal on 

 a large scale and label the appendages and other parts 

 observed. 



Exercise 2. Draw a highly magnified view of one of the thoracic 

 appendages and label accurately all the parts. 



Internal organs. The digestive tract passes from the mouth, 

 which is ventrally placed and lies back of the ventral cleft in 

 the shell, first forward, then turns dorsally and finally posteri- 

 orly and extends back to the anus near the end of the abdomen. 

 Near the anterior bend of the digestive tract a pair of colored, 

 curved pouches communicate with it ; they are liver-sacs. The 

 sac-like heart may be seen beating rapidly above the intestine. 

 It possesses a pair of lateral openings into which the blood 

 streams from the body-cavity with each dilation, and an ante- 

 rior opening through which it is sent into the forward part of 

 the body with each contraction. There are no other blood 

 vessels. Below the heart is a pair of excretory glands, called 

 the shell glands, which open to the exterior near the mouth. 

 The nervous system consists of an optic ganglion and a brain, lying 

 back of the eye, and a ventral nerve containing seven ganglia. 



The reproductive organs. The daphnias which are usually seen 

 are all parthenogenetic females, the males making their appear- 

 ance at certain times of the year only. The female animal is 

 larger than the male, and may be distinguished by its brood-sac. 

 This is a large space just beneath the dorsal wall of the thorax 

 in which the eggs and the young brood are carried. The ovaries 

 are a pair of tubular organs alongside the intestine, which com- 

 municate, by means of short oviducts, with the brood-sac. The 



