THE METAMORPHOSIS. 419 



the same point. No one who speaks of the embryo of man passing 

 through the lower grades of the animal kingdom can have imagined that 

 man at any period was ever of his embryo life an infusorium, polypus, 

 muscle, snail, worm, crab, spider, insect, fish, turtle, snake, lizard, and 

 bird ; but the assertion is nothing more than that man as man has once 

 in the progress of his development been upon that grade upon which the 

 several classes beneath him remain stationary in the progressive deve- 

 lopment of the entire animal kingdom ; and Von Bar's proposition 

 expresses precisely the same thing, for in the successive development 

 of the animal kingdom there is found, just as in the development of 

 each individual animal, a progressive morphological and histological 

 separation as well as the gradual formation of a peculiar shape from 

 a more general one. The most general form of the Arthrozoon, as 

 which we have found the insect, is a body that is divided into rings 

 and segments ; and insects, therefore, must present us in their develop- 

 ment both with a progressive formation of a particular shape from this 

 more general one, as also with the morphological and histological 

 gradual perfection of their individual organs. The series of Gastrozoa, 

 as I succinctly call the first series, are, on the contrary, only so far 

 repeated by insects in their development as they themselves in their 

 own development have for object the progressive perfection of the 

 nutritive and propagative organs. This repetition, however, does not 

 extend to the external form, for this is the result of a new development 

 not yet visible in the Gastrozoa ; whereas the vertebrata which unite 

 in themselves both forms, viz. that of the Gastrozoa as well as of the 

 Artkrozoa, exhibit also formal approximations to the Gastrozoa in 

 their development. Only so long as it remains in the egg-case is 

 every insect a Gastrozoon, for it then has no other organs than the 

 nutrimental ; but upon quitting the egg-shell it becomes an Arthro- 

 zoon, and exhibits itself in its then appropriate jointed shape. 



250. 



Hence, therefore, the essential character of the metamorphosis of 

 insects is found in the repetition of the lower grades of the Arthrozoa 

 by means of the development of the highest. No single class of 

 animals, we might say, confirms this repetition more distinctly than 

 insects. The maggot, caterpillar, or larva which creeps out of the egg 

 is of the same form as the earth-worm. Some of these maggots are 

 footless and headless, and move like the leech by affixing the first and 



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