ORDER BRANCHIOPODA. 339 



entirely occupied by a large eye ; their feet are completely 

 uncovered. 



As yet we know but a single one, the Polyphemus of ihe 

 ponds, Monocuhis pediciilus, Linn. Deg. Insect. VII. xxviii, 

 6 — 13 ; Polyphemus oculus, Mull., &c. 



According to Jurine, the feet in no respect resemble those 

 of the monoculi of this division. They are composed of a 

 thigh, a leg, a tarsus with two articulations, and from the 

 extremity of which come forth (that of the last pair excepted), 

 some small filaments. From the anterior extremity of the head 

 some smallantennajproject, of a single articulation, terminated 

 by two filaments. The shell is so transparent, that all the vis 

 cera may be distinguished through it. The matrix, vs-hen it is 

 full of eggs, occupies the major part of the interior of this shell. 

 Their largest number does not exceed ten. When we trace 

 the gradual development of the foetus, we are struck by the 

 prompt appearance of the eye, comparatively to that of the 

 other parts of the body : it is at first greenish, and passes in- 

 sensibly to deep black. The abdomen, after being convoluted 

 on itself, from behind forwards, folds suddenly backward to 

 form a long, narrow, and pointed tail, from which come 

 two long articulated filaments. The animal always swims 

 upon its back, and most frequently horizontally, communi- 

 cating to its arms or oars, and to its feet, lively and reiter- 

 ated movements. It executes, with considerable nimbleness 

 and agility, all sorts of evolutions. It is subject, in its youth, 

 and after its first moultings, to a malady called ephippium, 

 but this ephippium or saddle has always a determinate figure, 

 and never contains the two oval balls, which it presents in 

 daphnia. In a state of captivity, this animal will not live 

 long, and the young cannot be reared, at least Jurine could 

 not preserve them after the first moultings, nor observe the 

 progress of their generations. He did not recognize males in 

 any of the individuals which he kept ; in fact, he was able to 



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