WORMS AND CRUSTACEA. 219 



and about the junction of the lateral halves of the collar, and 

 which exhibits such a high degree of sensitiveness. 



The reproductive system consists of an egg-bearing portion (ov) 

 and the emptying conduit, (ov 1 , ov 2 , ov*,) or matrix, as it is called. 

 The former is an elongate narrow mass, with an irregular surface, 

 which stretches along the lower median line of the body, from 

 its posterior end to its middle, and just above the main nervous 

 cord. The matrix (ov 1 ) is a hollow, spindle-shaped body which 

 opens (ov 2 ) exteriorly not far behind the mouth, and close to 

 the main nervous cord, (#,) either just to the right or the left 

 of it. Not far from this outlet a trumpet-shaped body (ou 3 ) 

 projects from the upper side of the matrix. The trumpet is 

 hollow, and forms a means of communication between the cav- 

 ity of the body and the interior of the matrix, and thence with 

 the exterior. When, therefore, the eggs are dropped from the 

 ovary (ov) they float freely in the body cavity, and in process 

 of time are taken up by the trumpet and passed into the matrix, 

 and by that are cast out, through its inferior opening, (ov 2 ,) into 

 the surrounding element. 



The various transitions of form from the lower to the higher 

 groups are so clearly exhibited to the eye among the Articulata, 

 that I would be glad to find time to illustrate all the details of 

 the series of changes which the organs pass through in order to 

 arrive at the most elevated ranks of organization ; but I must 

 content myself with a mere indication of some of the great 

 steps, regarding only the more superficial parts of the body. 



The Crustacea, such as shrimps, lobsters, and crabs, stand 

 next in rank above the Worms. In this group, or class, as it is 

 called, we find, as we pass from the simpler to the more highly 

 organized, i. e. from the shrimps to the lobsters and thence to 

 the crabs, that the tendency is to mass or concentrate the body 

 in front, and thin it out behind. Those Crustaceans which 

 stand lowest in this class exhibit this tendency by a lengthen- 

 ing of the anterior rings of the body, as is shown in this fig- 

 ure, (fig. 128,) forming what is called a head-chest, or cephalo- 

 tliorax (cr). Eventually, as we ascend the scale, we find this 



