THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 96. DECEMBER 1865. 



XLII. — On the Systematic Value of the Organs which have been 

 employed as Fundamental Characters in the Classification of 

 Mollusca. By Dr. 0. A. L. Morch. 



Whether classes, orders, and genera are founded in nature, or 

 are only artificial divisions, is a question rarely disputed. It is, 

 however, still a matter of discussion whether now-existing spe- 

 cies are direct descendants of extinct forms from remote geo- 

 logical periods, which have been gradually changed in the course 

 of natural selection or in consequence of physical changes of the 

 globe, or are entirely new creations of any one geological era. 

 The habits of an animal often cause a considerable modification 

 of the external form, size, or colour, which are often improperly 

 considered of specific value ; but it must be admitted that such 

 difierences are subject to limits which cannot be passed, and do 

 not become hereditary. For instance, the corns of the human foot 

 are, like the nails, a thickening of the epidermis ; but the former 

 are produced by accidental pressure on the foot, while the latter 

 originate in the fcetal structure of the animal. There is the 

 same distinction between false and genuine species. 



Linne divided all creation into three kingdoms — animal, 

 vegetable, and mineral. The last-named division is less logical, 

 because minerals can only be considered as parts of the great 

 celestial bodies, which may be regarded as inorganic beings with 

 involuntary motion impressed upon them, corresponding with 

 that of the heart or stomach of animals. Geofiroy St.-Hilaire 

 has more correctly made the division into phanerobiotic and 

 cryptobiotic kingdoms. A predestined scheme is shown in the 

 chronology of our planet as well as in the development of organic 

 beings. Thus the oceans with their lower types are regularly 

 in course of time changed to islands and continents with their 



Ann. is Mag. N. Hist. Ser.3. Fo/.xvi. 26 



