SUMMARY OF MORPHOLOGICAL DEVELOPMENT. 233 



cases temporary aggregates of such like individuals; and in 

 other cases permanent aggregates of them: certain of which 

 become so definitely integrated that the individualities of 

 their component members are almost lost in a tertiary indi- 

 viduality. 



Along with this progressive integration there has gone on 

 a progressive differentiation. Vegetal units of whatever 

 order, originally homogeneous, have become heterogeneous 

 while they have become united. Spherical cells' aggregating 

 into threads, into laminae, into masses, and into special tis- 

 sues, lose their sphericity; and instead of remaining all 

 alike assume innumerable unlikenesses — from uniformity 

 pass into multiformity. Fronds combining to form axes, 

 severally acquire definite differences between their attached 

 ends and their free ends; while they also diverge from one 

 another in their shapes at different parts of the axes they 

 compose. And axes, uniting into aggregates of a still higher 

 order, become contrasted in their sizes, curvatures, and the 

 arrangements of their appendages. Similarly among 



animals. Those components of them which, with a certain 

 license, we class as morphological units, while losing their 

 minor individualities in the major individualities formed of 

 them, grow definitely unlike as they grow definitely com- 

 bined. And where the aggregates so produced become, by 

 coalescence, segments of aggregates of a still higher order, 

 they, too, diverge from one another in their shapes. 



The morphological differentiation which thus goes hand 

 in hand with morphological integration, is clearly what the 

 perpetually-complicating conditions would lead us to antici- 

 pate. Every addition of a new unit to an aggregate of such 

 units, must affect the circumstances of the other units in all 

 varieties of ways and degrees, according to their relative 

 positions — must alter the distribution of mechanical strains 

 throughout the mass, must modify the process of nutrition, 

 must affect the relations of neighbouring parts to surround- 

 ing diffused actions; that is, must initiate a changed inci- 



