Comparative Physiology. 205 



EXOGENS ENDOGENS. 









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ACROGENS. 



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FERNS, ETC. 



PROTOPHYTA. 



FUNGI. 



" Starting from the simplest algae and lichens, which re- 

 semble one another closely in every respect, unless their locality, 

 and which are classed under the general name of Protophyta or 

 simplest plants, we may pass on the one side, through the 

 Hepaticfe and mosses to the ferns, the highest among the 

 Acrogens, or Cryptogamia. From mosses and ferns the transi- 

 tion is easy, through the Lycopodiacea3 (club mosses) and Gym- 

 nospernije (Coniferse, &c.), to Exogens. Exogens and Endogens 

 have many connecting links ; and, from the latter group, the re- 

 turn to the fungi is direct by the Rhizanthese, whilst the simplest 

 forms of the fungi bring us back again to the Protophyta." 



In the next chapter, he traces the connection between the 

 diiferent groups of animals and the manner in which their af- 

 finities unite and separate, showing the connecting link between 

 the lower and the higher, and their gradual approximation to 

 one another. In tracing the manner in which the grand divisions 

 are connected, and enquiring how far these divisions may be re- 

 garded as analogous to those of plants, he expresses their affini- 

 ties as passing from Phytozoa the simplest forms of animal 

 structure, through MoUusca and Cephalopoda, to Vertebrata the 

 highest in the scale, and returning by Articulata, through Hq- 

 lothuridte and Hadiata, to Phytozoa again. If these divisions 

 be admitted, he says, " as expressing the principal types of 

 structure, a very curious series of analogies may be pointed out, 

 which indicate their correspondence with those of vegetables. In 

 making such comparisons, it should be carefully kept in mind 

 that we must not expect to find among plants any characters 

 analogous to those peculiar to the animal kingdom ; and that we 

 must be guided, rather by the general plan of structure and 

 arrangement of the organs, than by any of those details which, 

 in the higher classes of animals especially, are so much modified 

 by their connexion with the function of relation. Perfection 

 in the vegetable kingdom having reference to the nutritive 

 system alone, whilst among animals it is the manifestation, in 

 the highest degree, of the powers of sensation and locomotion, 

 and of the psychial faculties connected with them. Keeping 

 these pi'inciples in view, we proceed to point out the affinity 



3d Ser. 1843. — V. r 



