Uoyal Institution, 211 



found, as the relation of polarity prepares us to expect, animals so 

 nearly resembling sea- weeds, as often to be confounded with them. 

 These are found to be a multitude of individuals, arranged in a defi- 

 nite form on a common axis. To these branch-like beings, constitu- 

 ting the entirety of the zoophyte, vesicles are suspended, containing 

 eggs, in cup- shaped bodies of various and beautiful forms. Professor 

 Forbes discovered, from a series of elaborate researches in the genus 

 Plumularia, that there was the same analogy between this polype- 

 vesicle and the creature which produces it, that there is between the 

 green leaf and the flower and fruit of the plant. This proposition 

 the Professor illustrated by instancing six orders of zoophytic form, 

 in which this metamorphosis was distinctly traceable. 



Having thus developed his views on morphological analogy, that 

 of combination, Prof. Forbes entered upon what he admitted to be a 

 more doubtful part of his system — the analogies between parallel 

 groups. Having noticed that organized beings are grouped in types, 

 the members of each type being formed on the same model, he de- 

 clared his opinion that the members of every type which differ from 

 the typical form, differ by adopting the characteristic of the nearest 

 type. Thus, assuming the MoUusca and Annelida to be parallel 

 types, the Pectenibranchous gasteropod, which is typical of the 

 former, comes into the same group with the shell-less, worm-like 

 nudibranch, which possesses so many of the external characteristics 

 of the latter. [The Professor here laid great stress on the difference 

 between analogy, which chiefly regards form, — and affinity, which 

 respects structure and function.^ 



Again, in the case of species, whenever any individual of any spe- 

 cies of one group becomes monstrous as to number, this monstrosity 

 is shown by assuming the dominant number of the corresponding 

 group. Thus, the Arachnoderms and Echinoderms are in this rela- 

 tion of parallelism (the former having their organs arranged in mul- 

 tiples of four, the latter in multiples of five). Now, according to 

 Prof. Forbes, whenever a monstrous example of either tribe occurs, 

 the number assumed is that of the parallel tribe (four in the case of 

 Echinoderms, and^'ve in that of Arachnoderms). 



Again, throughout the parallel groups of nature there is a mutual 

 representation of each other's characteristics. Thus, the animal is 

 characterized by concentration of essential parts, and by being or- 

 ganized with a view to the development of the individual : the vege- 

 table is characterized by elongation of essential parts, and by being 

 organized with a view to extensive reproduction of the species. In 

 proportion as the animal approaches the vegetable, it does so by as- 

 suming the vegetable characteristics. Thus, while there is a ten- 

 dency to concentration (animal characteristic) in Vertebrata, there is 

 a tendency to extension (vegetable characteristic) in Articulata. 

 Again, there is an universal tendency to the formation of an endo- 

 skeleton in Vertebrata, and of an ea:o~skeleton in Articulata ; so, in the 

 higher plants, there is a tendency to an endo- skeleton and concentra- 

 tion in the exogens, to an exo-skeleton and extension in the endogens. 

 These principles were illustrated by these, among other examples : — 

 The Gasteropodous moUusca contain the Patella and Chiton ; the one 



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