5S6 APPENDIX A. 



work ; we cannot lielp admitting that tlie aggregative and sepa- 

 rative tendencies do in each case determine the respective de- 

 velopments of the individual and the race. On ascending one 

 degree in the scale of organic life, we shall find this truth clearly 

 exemplified. 



For if these single-celled organisms which multiply so rapidly 

 be supposed to lose some of their separative tendency, what 

 must be the result ? They now not only divide frequently, but 

 the divided portions fly apart. How, then, will a diminution of 

 this separative tendency first show itself ? May we not expect 

 that it will show itself in the divided portions not flying apart, 

 but remaining near each other, and forming a group ? This we 

 find in nature to be the first step in advance. The lowest com- 

 pound organisms are " simple aggregations of vesicles without any 

 definite arrangement^ sometimes united, but capable of existing sepa- 

 ratelyy * In these cases, " every component cell of the aggre- 

 gate mass that springs from a single germ, being capable of 

 existing independently of the rest, may be regarded as a distinct 

 individual." \ The several stages of this aggregation are very 

 clearly seen in both the animal and vegetable kingdoms. In the 

 Hcematococcus binalis, the plant producing the reddish slime seen 

 on damp surfaces, not only does each of the cells retain its 

 original sphericity, but each is separated from its neighbour by a 

 wide interval filled with mucus ; so that it is only as being 

 diffused through a mass of mucus common to them all, that these 

 cells can be held to constitute one individual. We find, too, that 

 "the component cells, even in the highest Algae, are generally 

 separated from each other by a large quantity of mucilaginous 

 intercellular substance." J And, again, the tissue of the simpler 

 Lichens, "in consequence of the very slight adhesion of its 

 component cells, is said to be pulverulent." § Similarly the 

 Protozoa, by their feeble union, constitute the organisms next 

 above them. Amongst the Polygastrica there are many cases 

 " in which the individuals produced by fission or gemmation do 

 not become completely detached from each other." f The Oph- 

 rydium, for instance, " exists under the form of a motionless jelly- 

 like mass . . . made up of millions of distinct and similar 

 individuals imbedded in a gelatinous connecting substance ; " ^ 

 and again, the Uvella, or " grape monad," consists of a cluster 

 " which strongly resembles a transparent mulberry rolling itself 

 across the field of view by the ciliary action of its component 

 individuals." '^^ The parenchyma of the Sponge, too, is made 



* Carpenter. f Prin. of Phys.^ p. 8Y3. 



Ibid , p. 203. p Ibid., p. 209. 



Ibid., p. 249. 1i Ibid., p. 249. 



** Ibid., p. 250. 



