6 MORPHOLOGICAL DEVELOPMENT. 



tion, the homologies of its different parts become problems. 

 Under the disguises induced by the consolidation of primary, 

 secondary, and tertiary units, it has to be ascertained which 

 answer to which, in their degrees of composition. 



Such questions are more intricate than they at first ap- 

 pear ; since, besides the obscurities caused by progressive inte- 

 gration, and those due to accompanying modifications of form, 

 further obscurities result from the variable growths of units 

 of the different orders. Just as an army may be augmented 

 by recruiting each company, without increasing the number 

 of companies; or may be augmented by making up the full 

 complement of companies in each regiment, while the num- 

 ber of regiments remains the same; or may be augmented 

 by putting more regiments into each division, other things 

 being unchanged; or may be augmented by adding to the 

 number of its divisions without altering the components of 

 each division; or may be augmented by two or three of these 

 processes at once; so, in organisms, increase of mass may 

 result from additions of units of the first order, or those of the 

 second order, or those of still higher orders ; or it may be due 

 to simultaneous additions to units of several orders. And 

 this last mode of integration being the general mode, puts 

 difficulties in the way of analysis. Just as the structure of 

 an army would be made less easy to understand if companies 

 often outgrew regiments, or regiments became larger than 

 brigades; so these questions of morphological composition 

 are complicated by the indeterminate sizes of the units of 

 each kind: relatively-simple units frequently becoming more 

 bulky than relatively-compound units. 



§ 177. The morphological problems of the second class 

 are those having for their subject-matter the changes of shape 

 which accompany changes of aggregation. The most general 

 questions respecting the structure of an organism, having been 

 answered when it is ascertained of what units it is composed 

 as a whole, and in its several parts; there come the more 



