STATE GEOLOGIST. 23 



the animal is covered by a jelly-like mass secreted as a protection 

 or float. The antennae are simple in the female and extend 

 through a slit in this covering. In the male they are prehensile 

 and have rudimentary inner rami. It would be difficult to recog- 

 nize the affinity of the female with its monstrous form were it not 

 for the male and particularly the development history. Found in 

 this state probably only in lake Superior. Forbes mentions it from 

 lake Michigan. 



FAMILY DAPHNIDJE. 



The family Daphnidse contains the genera Moina, Ceriodaphnia, 

 Scapholeberis, Simocephalus and Daphnia, which include the com- 

 monest, as well as some of the largest, Cladocera. The genera may 

 be distinguished by the following table: 



I. Head rounded, not beaked; antennules long iu both sexes, shell 



not covering the end of the abdomen Moina. 



II. Head rounded ; antennules rather short ; shell enclosing whole 



body Ceriodaphnia. 



III. Head somewhat beaked below, shell angled below or extending 



in long spines from the lower angle, pigmentfleck roundish.. .Scapfioleberis. 



IV. Head beaked below ; shell rounded below, with a blunt spine 



above : pigmentfleck elongate Simocephalus. 



V. Head beaked below ; shell extending in a sharp spine at the upper 



posterior angle ; pigmentfleck small Daphnia, 



The Circulatory System of the Daphnid^. 



In the Daphnidce, and, indeed, the Cladocera in general, we meet 

 an instance of great development of surfaces at the expense of 

 solidity of form and compactness of organs. The whole body is 

 composed of an aggregate of laminae, and the appendages all ap- 

 proximate more or less toward this fundamental modification. 

 Thus, for example, the head is a leaf-like body with a laminate shield 

 above and a pair of flat organs beneath. The abdomen terminates in 

 a knife-like post-abdomen, while the thorax, with its narrow form, 

 foliaceous feet and, far more, the enormous development of the 

 outer wall to enclose, more or less fully, the entire body, is the 

 typical illustration of this fact. Necessarily this structural modi- 

 fication exerts a formative influence on the internal organs which 

 are all more or less influenced by it* and this is peculiarly the case 

 with the more external and, in general, the paired organs. Thus 

 the " shell glands," so called, which in Copepoda are generally 

 coiled tubes, become here greatly flattened organs closely united 

 with the shell. The physiological result of this modification is the 



