Comjmrative PInjsioloc/i/. 383 



higher plants, those functions are confined to certain portions of 

 the surface. The leaves and roots of the higher plants have a 

 functional analogy with the simple membrane of the algae, 

 which absorbs and respires. Even In the highest animals, the 

 organs adapted to those functions are essentially com^^osed of a 

 simple membrane, a jDrolongatlon of the external surface. The 

 respiratory organs of plants are prolonged externally, like the 

 gills of fishes : in terrestrial animals they are Intei-nal ; the 

 membrane of the tubes or cells exposing a large surface. The 

 absorbing organs of plants are prolonged into the soil, while In 

 animals they are distributed upon the Avails of a cavity, fitted 

 to prepare and retain the food. Still the same fundamental 

 unity exists, and the sjjongloles In vascular plants, and the 

 absorbent vessels In animals, have precisely the same essential 

 character with the membrane which constitutes the general 

 surface of the sea-Aveed and red snow. Throughout the Avhole 

 animated creation, the essential character of the organs which 

 all possess in common remains the same ; whilst the mode in 

 Avhich that character Is manifested varies with the general plan 

 uj^on which the being is constructed. 



" In the early stages of formation In organised beings of the 

 higher classes, before the structure has been progressively de- 

 veloj)ed, we may observe as great a dissimilarity to Its ultimate 

 condition, as exists between the lower and higher classes. In 

 the progress of developement we may trace a correspondence 

 between the advance of the germ to maturity, and the ascent of 

 the different races as they rise in their permanent condition In 

 the scale of creation. The functions are more specialised, not 

 so general ; and there is a greater variety of dissimilar parts in 

 the higher organisms than in the lower ; the lower are more 

 homogeneous, the higher more heterogeneous. A heterogeneous 

 or special structure arises thus out of one more homogeneous 

 or general, and this by a gradual change. When the different 

 functions, however, are highly sj^eclallsed, the general structure 

 retains more or less the primitive homogeneity of function which 

 originally characterised it. The doctrine of the correspondence 

 between the transitory forms exhibited by the embryos of higher 

 beings, and the permanent conditions of the lower, refers to 

 individual organs alone, and not to the Avhole structure. The 

 higher animals and vegetables can never be mistaken for those 

 of the lower classes, thovigh the progress of individual organs 

 from a general to a special type Is discernible in the develope- 

 ment of the embryo, as well as In the ascending scale. Eccen- 

 tric developement explains the malformations from arrestment 

 of developement in the higher animals, causing monstrosity. 

 The study of monstrosities In the vegetable kingdom has 

 been peculiarly effectual in the elucidation of the laws regulat- 



c c 2 



