20 GENERAL PRINCIPLES OF ZOOLOGJ. 



comprehensible to his mental cajiabilities ? Are the specific and 

 generic names only expressions which have become necessary, from 

 the nature of our mental capacity, for the gradation of relation- 

 ship in nature, which in and for themselves are not immutable, 

 and hence can undergo a gradual change ? Practically speaking, 

 the problem reads : are species constant or changeable ? What is 

 true for species must necessarily be true for all other categories of 

 the system, all of which in the ultimate analysis rest upon the 

 conception of species. 



Ray's Conception of Species. — One of the first to consider the 

 conception of species was Linnseus's predecessor, the Englishman 

 John Eay. In the attempt to define what should be understood 

 as a species he encountered difficulties. In practice, animals which 

 differ little in structure and appearance from one another are 

 ascribed to the same species; this j^ractical procedure cannot be 

 carried out theoretically; for there are males and females within 

 the same species which differ more from one another than do the 

 representatives of different species. Thus .John Kay reached the 

 genetic definition when he said: for plants there is no more 

 certain criterion of specific unity than their origin from the seeds 

 of specifically or individually like plants; that is to say, generalized 

 for all organisms: to one and the same species belong individuals 

 which spring from similar ancestors. 



The < Cataclysm Theory.'— T\^ith Eay's definition an entirely 

 uncontrollable element was brought into the conceijtion of species, 

 since no systematist usually knew anything, nor indeed could he 

 know anything, as to whether the representatives of the species 

 placed before him sprang from similar parents. It was therefore 

 only natural that the conception of species put on a religious garb, 

 since by resting upon theological ideas it found a firmer support. 

 LinniBus said : " Tot sunt species cpiot ab initio creavit infinitum 

 Ens"; with this he built up a conception of species upon the 

 tradition of the Mosaic history of creation, a procedure quite 

 unjustified upon grounds of natural science, since it drew one of 

 its fundamental ideas from transcendental conceptions, not from 

 the experience of natural science. Linn;T?us's definition showed 

 itself untenable, as soon as paleontology began to make accessible 

 a vast quantity of extinct animals deposited as fossils. With an 

 odd fancy, the fossils, lieing inconvenient for study, were for a 

 long time regarded as outside the pale of scientific research. They 

 might be sports of nature, it was said, or remains of the Flood, or 

 of the influence of the stars upon the earth, or products of an aura 



