82 MOKPHOLOGICAL DEVELOPMEyX. 



component tmits remain quite distinct. Being, as aggro* 

 gates of tlie first order, mncli more definitely organized, 

 their union into aggregates of tlie second order does not de- 

 stroy tlieir original indiAddufdities, Among tlie VorticelLSi 

 of wliich. two kinds are delineated in Figs. 144 and 145, there, 

 are various illustrations of this : the members of the com- 

 munity being sometimes appended to a single stem ; some** 

 times attached by long separate stems to a common base ; and 

 sometimes massed together. 



Thus far, ihesQ aggregates of the second order exhibit but 

 indefinite individualities. The integration is physical ; but 

 not physiological. Though, in the Thalassicollce, there is a 

 shape that has some s^mametry ; and though, in the Fora- 

 77iifiif era, the formation of successive chambers proceeds in such 

 methodic ways, as to produce qiute-regular and tolerably- spe- 

 cific shells ; yet no more in these than in the Sponges or the 

 compoimd Yorticellce, do we find such co-ordination as gives 

 the whole a life predominating over the lives of its parts. 

 We have not yet reached an aggregate of the second order, 

 so individuated as to be capable of sef^-ing as a unit in still 



higher combinations. But in 

 ^/ _ the class Ccelenterata, this ad- 



^vi (^iii Vance is displayed. The com- 

 \ ^1 5 3/ ^ mon Hijdra, habitually taken as 

 Jo fp^^ the type of the lowest division 

 '^j' --y of this class, has specialized 

 parts performing mutually-subservient fimctions ; and thus 

 exhibiting a total life distinct from the lives of the units. 

 Fig. 146 represents one of these creatures in its contracted 

 state and in its expanded state ; while Fig. 147 is a 

 rude diagram from memory shomng the wall of this 

 creature's sack-like body as seen in section under the 

 microscope : a and h being the outer and inner cellular 

 layers ; while in the central space between them, is 

 that nucleated substance, or sarcode, or protoplasm, 

 in which the cells originate. But this lowly- organized 



