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- 



