common to North America and Europe. 481 



except Sicily ; Pisidium appendiculatum in England and 

 Sweden ; and Limnea palustris in Ireland, England, Scot- 

 land, Mona, Germany, Sv^eden, and Corsica.* 



After the authorities I have cited in favor of a community 

 of species between distant regions, I think it indicates a con- 

 siderable degree of boldness to deny the identity of objects 

 never seen, on the strength of a preconceived opinion, which, 

 if true, (and I am far from making the remark as argument 

 against it) v/ill destroy much of the interest with which 

 geographic zoology and botany are invested, and originate a 

 more untenable theory than that of appetency ; for, according 

 to the latter, after a fish would have become a bird, it would 

 be a bird ; but, according to the former, it would still be a 

 fish;-|- Cynthia cardui would be from three to seven species, 

 according to the extent of country required to constitute a 

 zoological region, as it inhabits North America, South Amer- 

 ica, Europe, Northern, Western, and Southern Africa, the 

 Islands of Madagascar and Bourbon, Bengal, China, Java, 

 and Australia ; and Colias edusa, another frail butterfly, 

 would, in like manner, become four species, on account of 

 its occurrence in North America, Europe, Caffraria, and Nipal. 



In connection with this subject, I wish to protest against 

 the practice of making distinct species of similar organic re- 

 mains, merely because they are found in different strata or 

 formations — a proceeding which must end in the admission 

 that a genus can contain more species than distinct forms, 

 (which involves a contradiction) and, indeed, an infinite 

 number of species. There must, however, be a limit to spe- 

 cies, and the limit must vary with the genera ; because an 

 insect, having more organs than a worm, affords a greater 



* Grav's Turton, p. 30. Mr. Lea has a beautiful and extensive series of Alasmo- 

 don margariliferus, from various parts of Europe and America, including Columbia 

 River. 



t Tbi? inference is fairly deducible from the writings of Dr. Prichard, and others 

 of the same school, some of whom are continually making attacks upon Lamarck, 

 for the general or uncritical reader, in a manner ingeniously calculated to keep the 

 merits of the question out of view. It is a matter of congratulation to the friends 

 of the French philosopher, that he never produced anything approaching this in 

 absurdity. 



54 



