XL] SPECIFIC GENESIS. 253 



kingdoms. A curious resemblance, though less in degree, 

 has also been seen to exist between the auditory organs of 

 tishes and of Cephalopods. Eemarkable similarities between 

 certain placental and implacental mammals, between the 

 bird's-head j)i'ocesses of Polyzoa and the pedicellarise of 

 Echinoderms, between Ichthyosauria and Cetacea, with 

 very many other similar coincidences, have also been 

 indicated as instances in point. 



Evidence has also been brought forward to show that 

 similarity is sometimes directly induced by very obscure 

 conditions, at present quite inexplicable, e.g. by causes 

 immediately connected with geographical distribution ; as 

 in the loss of the tail in certain forms of Lepidoptera and 

 in simultaneous modifications of colour in others, and in 

 the direct modification of young English oysters when 

 transported to the shore of the Mediterranean. 



Again, it has been asserted that certain groups of organic 

 forms seem to have an innate tendency to remarkable de- 

 velopments of some particular kind, as beauty and singu- 

 larity of plumage in the group of birds of paradise. 



It has also been contended that there is something to 

 be said in favour of sudden, as opposed to exceedingly 

 minute and gradual, modifications, even if the latter are 

 not fortuitous. Cases were brought fgrward, in Chapter IV., 

 such as the bivalve just mentioned; twenty-seven kinds 

 of American trees simultaneously and similarly modified; 

 also the independent production of pony breeds; and the 

 case of the English greyhounds in Mexico, the offspring 

 of which produced directly acclimated progeny. Besides 

 these, the cases of the Normandy pigs, of Datura tatula, 

 and also of the black-shouldered peacock, have been spoken 

 of The teeth of the labyrinthodon, the hand of the potto, 



