354

ESSAY ON CLASSIFICATION.

organic functions of life are carried on in antagonisticrelations, from the centre to the circumference. Corre-sponding to this, the whole organization radiates arounda common centre. There exists, besides, only the contrastbetween above and below, but in a weaker degree; thatbetween right and left, or before and behind, is not at allnoticeable, and the motion is therefore undetermined inits direction. As the whole organization radiates fromone focus, so are the centres of all the organic systemsarranged, ring-like, around it; as, for instance, the sto-mach, the nerves and the vessels (if these parts are deve-loped), and the branches extending from them into therays. What we find in one ray is repeated in every other,the radiation being always from the centre outwards, andevery ray bearing the same relation to it.

II. The Longitudinal Type, as observed in the Vibrio,the Filaria, the Gordius, the Nais, and throughout thewhole series of articulated animals. The contrast betweenthe receiving and the discharging organs, which are placedat the two ends of the body, controls the whole organiza-tion. The mouth and the anus are always at oppositeends, and usually also the sexual organs, though theiropening is sometimes farther forward: this occurs, how-ever, more frequently in the females, in which these organshave a double function, than in the males. When bothsexual organs are removed from the posterior extremity,the opening in the female usually lies farther forward thanin 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 organsof senses, as instrumental to the reception of the ner-vous system, early reach an important degree of perfec-tion. The intestinal canal, as well as the vascular stems