THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 



83 



tissue of the Hydra, illustrates a phase of integration in 

 which the lives of the minor aggregates are only par- 

 tially-subordinated to the life of the major aggregate 

 formed by thom. For a Hydra's substance is separable into 

 4wce&a-like portions, capable of moving about independ- 

 ently. Prof. Grreen quotes Ecker, Lewes, and Jager, in proof 

 that " this animal exhibits, at certain seasons of the year, a 

 tendency to break up into particles of a sarcode aspect, which 

 retain for a long time an independent vitaKty." And if we 

 bear in mind how analogous are the extreme extensibility 

 and contractility of a Hydra's body and tentacles, to the pro- 

 perties displayed by the sarcode among Rhizopods ; we may 

 infer that probably the movements and other actions of a 

 Hydra, are due to the half-independent co-operation of tho 

 Amaiba.-VikQ individuals composing it. 



§ 202. A truth which we before saw among plants, we 

 here see repeated among animals — the truth that as soon as 

 the integration of aggregates of the first order into aggregates 

 of the second order, produces compound wholes so specific in 

 their shapes and sizes, and so mutually dependent in their 

 parts, as to have distinct individualities ; there simultaneously 

 arises the tendency in them to produce, by gemmation, other 

 such aggregates of the second order. The approach towards 

 definite limitation in an organism, is, by implication, an ap- 

 proach towards a state in which growth passing a certain point, 

 results, not in the increase of the old individual, but in tho 

 formation of a new indi- 

 vidual. Thus it happens 

 that the common polype 

 bude out other polypes, 

 some of which very shortly 

 do the like, as shown in 

 Fig. 148 : a process paral- 

 .eled by the fronds of sundry Algce, and by those of the lo^rer 

 Jungermanniacece. And just as, among these last plants, the 



