176 AFFINITIES AND GEOGRAPHICAL 



the Creator, having a particular regard to the fact of inolluscan 

 shells lying useless on the shore, formed, by special care or 

 fiat, a family of crabs to occupy them. They must believe 

 that the roughness of the caudal appendages, the development 

 of suckers along the abdomen, the reduction of the two hind 

 pairs of limbs, and the left pincer-claw, were all subjects for 

 this special care, and were beyond the power of what an 

 eminent geologist calls " vulgar nature." Surely the Deus ex 

 machind was never more remarkably exemplified. See, on 

 the other hand, how these facts are accounted for on the de- 

 velopment theory. According to this new light, the hermit- 

 crabs are simply a portion of some greater section of the crus- 

 tacean class. Their peculiarities are modifications from the 

 parent form, brought about in the course of generations, in 

 consequence of an appetency which had led these creatures to 

 seek a kind of shelter in turbinate shells. They are as truly 

 creatures of the Great God, as if they had been made in the 

 manner of a human artist modelling a figure. But the means 

 were inherent natural forces in the constitution of the original 

 tribe, tending, in generation, to accommodate organic form, to 

 physical circumstances. 



The next class in general rank is the Insecta, a wonderfully 

 varied group, yet all agreeing in having thirteen segments and 

 three pairs of legs ; all, moreover, respiring by means of tracheae 

 or tubes permeating the body, an arrangement having re- 

 ference to their peculiar mode of locomotion, which, in the 

 majority of species, is by flight through the air. The fact of 

 the greater number of insect genera passing in their larva 

 state, through the annelidan or myriapodous form, points to 

 these classes as their genetic origin ; yet this is a point on 

 which the benefit of further investigation is desirable. In the 

 case of the Araclinida (mites and spiders), which are placed 

 at the head of the articulate class, no humbler fojm is traceable 

 in the embryo ; it is therefore impossible to assign them any 

 pedigree. Can it be possible that the arachnida, or these 

 with the insecta, have sprung almost or wholly at once from 

 inorganic elements ? On this subject, it is impossible to make 

 any positive affirmation ; but it certainly is remarkable that 

 in no department of the animal kingdom besides the infusoria 

 and entozoa, have there been more frequent appearances of an 

 aboriginal commencement of life than in the insecta. The 

 acarus, so often produced from certain solutions, where ova 

 were rigidly excluded, is a lowly member of the arachnida. 



