224 TnAysACTioys of the Ameeicax Isstitute. 



Tlie liydra moves bv its tentacles, and sucker-like extremity. 

 Many marine worms are provided with a series of little paddles, and 

 by their movements the animal is enabled to swim gracefully in the 

 water. 



Among the crnstaeea, it is very instructive to examine the func- 

 tions performed by appendages strangely modified to perform various 

 functions. 



In the incipient stages of the lol)ster, for example, the body is 

 composed of a series of rings, with appendages quite identical in 

 shape and size. In its growth the forward rings unite above and 

 form the carapace or shield, while in the hinder portion of the body 

 the rings remain separated so as to give full play to its movements. 

 It is by this portion that the lobster leaps backward in the Avater. 

 Beneath this portion are found little appendages that are flattened, 

 and form natatory organs by whieli they can swim. These append- 

 ages are also covered with hairs, and to these the eggs adhere when 

 discharged by the parent. The small claws are jointed, and are 

 used as legs by which they crawl, the two hinder pairs of claws hav- 

 ing but one projecting point, while the two forward pair of small 

 claws have a little pincer or nipper at the end. An examination 

 will show that no new feature is added to the claw, but simply an 

 excess in the growth of a portion of it, by which an opposing point 

 is made. The large claws are only an accessive development of a 

 similar appendage. Even the numerous organs around the mouth, 

 the feelers and eyes, are but modified feet. 



In insects we have for the first time animals tliat support themselves 

 by wings, those having broad wi?igs like the butterfly, moving them 

 slowly, while the bee, v.'ith small wings, moving them with incredi- 

 ble velocity. Tiine will again compel me to neglect the special 

 features in this group. We at last come to the vertebrates, as the 

 highest branch, and here the locomotive organs are reduced to two 

 pairs. In the lowest class, the fishes, these appendages are repre- 

 sented by the pectoral and ventral tins, and have little to do with the 

 propulsion of the animal. This is accomplished by the broad fin on 

 the tail, whicih is ra])idly moved from side to side, as a man in sculling 

 moves his oar. In the flying fish, the fins that represent the fore 

 legs arc greatly enlarged, and enable the fish to take short flight in 

 the air; while in another fish the same fins are developed into rude 

 legs, by which they creep over the mud. In the flounder a curious 

 mudilication takes place in the structure of the head. When first 



