INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 593 



together like bees or other gregarious creatures ; and to illustrate this 

 law it is necessary to refer to forms lower down in the scale in which 

 the component individuals are united to each other by a common 

 tissue. Accordingly, M. Perrier turns first to the Hydroids, and, 

 after referring to the budding of the Hydrce, shows that in compound 

 forms such as Cordylophora lacustris, and in most of the marine 

 Hydroids, what is only occasionally produced in Hydra becomes normal. 

 But a new phenomenon occurs — a veritable system of division of 

 labour is effected between the members of the same colony. At 

 first all were similar, all performed the same functions in the same 

 manner, but speedily each individual became specialized. One devotes 

 itself exclusively to the capture of food, another to the elaborating of 

 the nutritive material, and a third to reproduction, so that in the end all 

 these individuals, which originally had no need of one another, become 

 mutually necessary. Among the Hydractiniae we may reckon no fewer 

 than seven kinds of individuals fulfilling different functions. It might 

 seem to be an exaggeration to attribute the quality of individuals to 

 the different parts. We have here, it might be said, simple organs ; 

 but organs of what ? They are just as independent of each other and 

 of the nutritive individuals as the latter can be of one another. Hence 

 they are not organs of those polyps. Are we to see in them organs 

 of the colony ? This is at once to recognize that the colony has an 

 individual character, and consequently to assume the transformation 

 we seem to demonstrate. But how has a colony been able to acquire 

 such organs ? Whence can they have arisen if not from a transforma- 

 tion of the individuals composing it ? 



The author considers that there is no occasion for hypothesis in 

 order to demonstrate that these colonial organs are the equivalents of 

 true individuals. The buds which give origin to the different kinds 

 of individuals in a colony of Hydractinifc, all originate in the same 

 way, and are for a long time so similar that there is nothing to enable 

 them to be distinguished. In Podocoryne the humble sac which 

 represents the sexual individual is replaced by a Medusa much higher 

 in organization than the Hydra itself, which detaches itself on its 

 arrival at maturity. 



The same train of reasoning is applicable to the Siphonophora 

 and also to the Coralliaria, which are more highly organized and 

 exhibit a more complete amalgamation of the component individuals, 

 each of which in the Coralliarian polyp may be considered as a 

 number of Hydroid polyps rolled into one. 



This transforming of a number of individuals into one individual 

 can likewise be traced out in the Worms. Van Bencdcn established 

 that each of the joints of a tape-worm is the equivalent of a Trematode; 

 and, at a yet earlier period, naturalists considered the segments of 

 wonns and insects to be equivalent units, each having an actual 

 individuality, which they called zoonitcs. Sea-urchins and star-fishes 

 have also been looked upon as colonics of worms united by their 

 heads. 



Can we say the same of the Mollusca and Vertebrata, all the parts 

 of which seem to be so intimately fascd together? This is what 



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