138 THE INDUCTIONS OF BIOLOGY. 



same species, we discover the limit of gro wth to be much 

 less variable. Among the Protozoa and Protophyta, each 

 kind has a tolerably constant adult size ; and among the most 

 complex organisms the differences between those of the same 

 kind which have reached maturity, are usually not very 

 great. The compound plants do, indeed, sometimes present 

 marked contrasts between stunted and well-grown individ 

 uals; but the higher animals diverge but inconsiderably from 

 the average standards of their species. 



On surveying the facts with a view of empirically general 

 izing the causes of these differences, we are soon made aware 

 that by variously combining and conflicting with one another, 

 these causes produce great irregularities of result. It becomes 

 manifest that no one of them can be traced to its conse 

 quences, unqualified by the rest. Hence the several state 

 ments contained in the following paragraphs must be taken 

 as subject to mutual modification. 



Let us consider first the connexion between degree of 

 growth and complexity of structure. This connexion, being 

 involved with many others, becomes apparent only on so 

 averaging the comparisons as to eliminate differences among 

 the rest. Nor does it hold at all where the conditions are 

 radically dissimilar, as between plants and animals. But 

 bearing in mind these qualifications, we shall see that 

 organization has a determining influence on increase of 

 mass. Of plants the lowest, classed as Thallophytos, 



usually attain no considerable size. Alga3, Fungi, and the 

 Lichens formed by association of them count among their 

 numbers but few bulky species: the largest, such as certain 

 Algae found in antarctic seas, not serving greatly to raise the 

 average ; and these gigantic seaweeds possess a considerable 

 complexity of histological organization very markedly ex 

 ceeding that of their smaller allies. Though among Bryo- 

 phytes and Pteridophytes there are some, as the Tree-ferns, 

 which attain a considerable height, the majority are but of 

 humble growth. The Monocotyledons, including at one 



