322 CLASS CRUSTACEA. 



conduct by gradual shades to the lemscse ; but the presence of 

 eyes, the faculty of changing skin, or even of undergoing a 

 sort of metamorphosis, the power of being able to transport 

 themselves from one place to another by means of the feet, 

 appear to us to establish a positive line of demarcation be- 

 tween these last animals and the preceding. We have con- 

 sulted with respect to these transformations, different well 

 informed naturalists, who have had frequent occasions of ob- 

 serving the lernffise, and none have ever witnessed any 

 change of skin among them. It is true, indeed, that the 

 young of daphniae, and of some other neighbouring subgenera, 

 those probably also of cypris, and of cytherea, on issuing 

 from the egg, scarcely differ from their parents, except as to 

 size ; but those of cyclops, of phyllopus, of argula, undergo 

 notable changes in their early age, either in the form of the 

 body, or the number of the feet. In some, such as the argulae, 

 these organs even undergo transformations, which modify 

 their uses. 



The antennae of the entomostraca, the form and number 

 of which vary much, answer, in many of these animals, the 

 purpose of swimming. The eyes are very rarely supported on 

 a pedicle, and when they are, this pedicle is but a lateral 

 elongation of the head, and never articulated at its base. 

 They are often very closely approximated together, and often 

 compose but a single eye. The organs of generation are situ- 

 ated at the origin of the tail ; and it is erroneously that 

 the antennae of some males have been considered as the seat 

 of them. This tail is never terminated by a fan-like fin, and 

 does not present those false feet, which we have obsei'ved in 

 the malacostraca. The final feet, indeed — if we except the 

 phyllopoda — are thoracic, or jaw- feet. The eggs are accumu- 

 lated under the back, or they are external, and under a com-" 

 mon envelope, in the form of one or two small clusters, situated 

 at the base of the tail. It appears that they may be pre- 



