Vol. XII. 



WASHINGTON, D. C, DECEMBEK, 1892. 



No. 12. 



The Water-Flea : — Dapliiiia.' 



By THOS. KNOEBEL, Ph. G., 



EAST ST. LOUIS, ILL. 



This little creature, inhabiting both tresh and stagnant water, 

 belongs to the class of Crustacea, subclass Entomostraca, order 

 of Cladocera, and family of Daphniadae. Its color varies from a 

 pale straw color to a bright red. It would be a difficult matter to 

 find a more fitting and interesting subject for the microscope than 

 this little animal, measuring, when full grown, from 2 to 3^ mm. 



It has but one eye, five pairs of legs, two pairs of antennjE ; the 

 lower being branched and branchleted, and quite large and pow- 

 erful, are used as propellers in swimming. The head is length- 

 ened downward, forming a sort of a beak, presenting a rather 

 queer appearance. The body, excepting the head and antennae, 

 is enclosed in two delicate shells, oval shaped, resembling the two 

 halves of an English walnut, and, magnified about 25 diameters, 

 looks very much like fish-netting. 



Sexes are separate, the female being readily recognized by the 

 eggs, which are enclosed within the space between the shell and 

 body of the animal. The eggs are retained until the young are 

 fully developed, when they are allowed to escape from under the 

 covering. Have found from two to eleven young enclosed in 

 their temporary prison ; and by daily examination have found 

 specimens where the young were so far advanced as to be able to 

 move quite freely, seemingly making attempts to breakaway from 

 their little prison ; now, by carefully rupturing the cover of the 



•Read before the St. Louis Club of Microscopists, July 7, 1892. 



