248 ESSAY ON CLASSIFICATION 



extending from them into the rays. What we find in one ray is re- 

 peated in every other, the radiation being always from the centre 

 outwards, and every ray bearing the same relation to it. 



II. The Longitudinal Type, as observed in the Vibrio, the Filaria, 

 the Gordius, the Nais, and throughout the whole series of articulated 

 animals. The contrast between the receiving and the discharging 

 organs, which are placed at the two ends of the body, controls the 

 whole organization. The mouth and the anus are always at opposite 

 ends, and usually also the sexual organs, though their opening is 

 sometimes farther forward; this occurs, however, more frequently 

 in the females, in which these organs have a double function, than 

 in the males. When both sexual organs are removed from the pos- 

 terior extremity, the opening in the female usually lies farther for- 

 ward than in the male. So is it in the Myriapods and the Crabs. The 

 Leeches and Earthworms present a rare exception. The receptive 

 pole being thus definitely fixed, the organs of senses, as instrumental 

 to the receptivity of the nervous system, early reach an important 

 degree of perfection. The intestinal canal, as well as the vascular 

 stems of the nervous system, extend through the whole length of the 

 body, and all organic motion in these animals has the same prevail- 

 ing direction. Only subordinate branches of these organs arise later- 

 ally, and chiefly wherever the general contrast, manifested in the 

 whole length, is repeated in such a manner that, for each separate 

 segment, the same contrast arises anew in connection with the essen- 

 tial elements of the whole organism. Hence the tendency in these 

 animals to divide into many segments in the direction of the longi- 

 tudinal axis of the body. In the true Insects undergoing metamor- 

 phosis, these segments unite again into three principal regions, in the 

 first of which the life of the nerves prevails; in the second, motion; 

 in the third, digestion; though neither of the three regions is wholly 

 deprived of any one of these functions. Besides the opposition be- 

 tween before and behind, a less marked contrast is observed in a 

 higher stage of development between above and below. A difference 

 between right and left forms a rare exception and is generally want- 

 ing. Sensibility and irritability are particularly developed in this 

 series. Motion is active and directed more decidedly forward in pro- 

 portion as the longitudinal axis prevails. When the body is con- 

 tracted as in spiders and crabs, its direction is less decided. The plas- 



