Geographical Distribution of Crustacea. 47 



beyond what this cause might accomplish. Still, it cannot be 

 asserted that in all instances the distribution here is owing to 

 migration ; nor will it be admitted unless other facts throw the 

 weight of probability on that side. ; j 



IX. But when we find the same temperate zone species oc- 

 curring in distant provinces, these provinces having between 

 them no water-communication except through the torrid or 

 frigid zone, and offering no ground for the supposition that such 

 a communication has existed during the recent epoch, we are led 

 to deny the agency of voluntary or involuntary migration in 

 producing this dissemination. An example of this, beyond all 

 dispute, is that of the Mediterranean Sea and Japan. No water- 

 communication for the passage of species can be imagined. An 

 opening into the Red Sea is the only possible point of intercom- 

 munication between the two kingdoms ; but this opens into the 

 torrid zone, in no part of which are the species found. The 

 two regions have their peculiarities and their striking resem- 

 blances ; and we are forced to attribute them to original creation, 

 and not intercommunication. 



X. The resemblances found are not merely in the existence 

 of a few identical species. There are genera common to the 

 two seas that occur nowhere else in the Oriental kingdom, as 

 Latreillia, Ephyra, Sicyonia, &c. _; and species where not iden- 

 tical having an exceedingly close resemblance. 



Now this resemblance in genera and species (without exact 

 identity in the latter) is not explained by supposing a possible 

 intercommunication. But we may reasonably account for it on 

 the ground of a similarity in the temperature and other physical 

 conditions of the seas ; and the well-known principle of " like 

 causes, like effects," forces itself upon the mind as fully meeting 

 the case. Mere intercommunication could not produce the re- 

 semblance; for just this similarity of physical condition would 

 still be necessary. And where such a similarity exists, creative 

 power may multiply analogous species ; we should almost say, 

 mu^t ; for, as species are made for the circumstances in which 

 they are to live, identical circumstances will necessarily imply 

 identity of genera in a given class, and even of specific structure 

 or of subgenera. 



If then the similarity in the characters of these regions is the 

 occasion of the identity of genera, and of the very close likeness 

 in certain species (so close that an identity is sometimes strongly 

 suspected where not admitted), we must conclude that there is a 

 possibility of actual identity of species, through original creation. 

 This, in fact, becomes the only admissible view, and the actually 

 identical species between Japan and the Mediterranean are ex- 

 amples. 



