40 CHAPTERS ON EVOLUTION. 



II. MOLLUSCA (" soft-bodied " animals) (cuttle-fishes and " shell- 

 fish " at large). 



III. ARTICULATA (" jointed " animals) (insects, crustaceans, 

 worms, &c.). 



IV. RADIATA (" rayed " animals) (star-fishes, corals, jelly-fishes, 

 zoophytes, and all lower animals). 



Cuvier's own words, expressive of the nature of these types, may 

 be quoted : " It will be found that there exist four principal forms, 

 four general plans, if it may thus be expressed, on which all animals 

 appear to have been modelled ; and the ulterior divisions of which, 

 under whatever title naturalists may have designated them, are 

 merely slight modifications, founded on the development or addition 

 of certain parts." It may be added that the distinguished embry- 

 ologist Von Baer, attacking the problems of animal form from the 

 standpoint of development, and watching the phases observable in 

 the early history of animals as they advanced from the egg towards 

 their perfect forms, came to the same conclusion as the great French 

 anatomist. According to Von Baer, also, there were four types or 

 plans in the animal world, the distinctive nature of the type to which 

 any given animal belonged being indicated at an early stage in its 

 development. So that, as early as the beginning of the present 

 century, it became clear to the minds of naturalists that, instead of 

 each animal being built up on a type peculiar to itself, it fell into 

 one or other of four groups ; in a word, it was found to possess a 

 broad and fundamental plan or type of structure, with which a greater 

 or less number of other animals agreed. 



To render the " type " constitution of the animal world plainer 

 and more readily appreciated, we may select one or two examples 

 by way of illustrating, also, how, with the increase of knowledge 

 since Cuvier's days, the original types have remained stable in some 

 respects, whilst they have undergone modifications in others. No 

 two animals can well appear more varied in form, nature, appearance, 

 and habits and inferentially in structure likewise than a lobster 

 and a butterfly. The aerial habits of the one contrast very markedly 

 with the slow aquatic life of the other, whilst the general constitution 

 of the former appears to be separated by antipodean differences 

 from that of the other. Are there any bonds of common nature 

 which can link together beings so diverse ? and can the butterfly and 

 the lobster be shown to possess any relationships in common ? are 

 questions which it is reserved for the scientific but plainly understood 

 deductions of zoology to answer. The superficial examination of 

 the lobster would show that its body consists essentially of a 

 series of some twenty joints, each possessing a pair of appendages 

 modelled, despite their apparent differences, on one and the same 



