ENTOMOSTRACA. 



35 



FIG. 45. Bosmina striata. 



A rudimentary shell is present only in the female. It grows to be more than an 



inch in length, and is found in the open water of our great lakes as well as in Europe. 

 In the second sub-order, Calyptomera, the shell is well-developed, enveloping the 



limbs, and the ambulatory feet are broad, lamellar, and indistinctly segmented. The 



lowest family is the LYNCEIDJE, which has a short oval heart, a long, slender, convoluted 



intestine, very large antennae, both branches of which are three-jointed; and the legs, 



of which there are four or five pairs, are dissimilar, the hinder pair being the broadest. 



There are about nine or ten genera, the species of which are very small, few attaining 



a length of a twenty-fifth of an inch. They are 



mostly inhabitants of weedy shores and bottoms of 



the shallower parts of lakes and ponds. They are 



far less abundant than the Daphnice in temporary 



pools a fact, probably, due to their less perfect 



ephippium. But favorable localities swarm with 



them, swimming from weed to weed, burrowing 



about in vegetable debris, or rapidly whirling 



about on the calm surface. 



In the DAPHNID^E the heart is the same as in 



the last family, the intestine is short and straight, 



one branch of the antennae is three-jointed, the 



other four, while the pairs of ambulatory feet vary 



in the different genera, of which there are nearly twenty, from three to six. Of 



Daphnia, the typical genus, we have already spoken at considerable length. Bos- 

 mina is a form closely allied to 

 Daphnia. It is a beautiful genus, 

 having the antennulaa very large 

 and firmly attached to the head, 

 curving downward and backward 

 like the tusks of a walrus. The 

 species are very small and un- 

 usually transparent, so that the 

 microscope reveals at once their 

 whole anatomy. Hyaleodaphnia 

 is characterized by having the 

 front of the head greatly pro- 

 duced. 



The last family is the SIDID^E, 

 which has an elongate heart, a 

 short, straight intestine, and six 

 pairs of similar, lamellar legs. It 



contains eight genera, of which Penilia, Sida, and Latona are the most prominent. 

 The economic value of the Cladocera rests upon their astonishing fertility. Their 



numbers make up for their minute size, and they form no unimportant element in the 



food of our fresh-water fishes the smaller feeding greedily upon them, and as these 



in turn furnish food for the larger forms, the importance of the Cladocera and the 



Copepoda can readily be seen. 



E. A, BIEGE. 



FIG. 46. Hyaleodaphnia kerusses. 



