SLMMARY OF MORPHOLOGICAL DEVELOPMENT. 216 



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, be 

 come more or less contrasted in their sizes, curvatures, and 

 arrangements of their appendages. Similaiiy 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 

 dence of forces tending ever to produce changed structural 

 arrangements. 



