SLMMAKY OP MORPHOLOGICAL DEVELOPMENT. 216 



become so definitely integrated that the individualities of 

 their component members are almost lost in a tertiary indi- 

 viduaKty. 



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 stiU higher order, be- 

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

 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 ol 

 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 ; thut is, must initiate a changed inci- 

 dence of forces tending ever to produce changed structural 

 arran<rements. 



