482 POPULAR SCIENCE MONTHLY. 



genera as created, and species to have originated from them. When 

 the number of known species increased and soon assumed undreamed 

 of proportions, it seemed but natural not to accept for each species a 

 separate creation. But the others denied the possibility of a transi- 

 tion from an old form to a new one by natural means. Each actually 

 existing form, constant from seed, must, according to their idea, have 

 been created as such. They denied the right to collect groups of forms 

 under one specific name, as did Linnaeus and, after him, his disciples, 

 especially when, owing to constant research, an exceedingly large num- 

 ber of forms became known. Instead, they recognized each form as 

 a unity unities which could be collected under a generic name only. 



But Linnaeus, guided more by the talents of a lawyer than by 

 those of an investigator, had once for all connected his conception of 

 a species with the use of the binomials introduced by him. Whatever 

 bears two names is a species. This is the law which all must obey. 

 Genera bear simple names, subdivisions of species tri- or quadrinomials. 

 Whoever wishes to have a form recognized as a species, must give it 

 two names. Unless this be done he will not attain his object. But 

 the number of simple forms, constant from seed, increased year by 

 year and, even for Europe alone, threatened to become ten times 

 greater than it had been. 



Since the validity of the theory of descent has been generally rec- 

 ognized, these questions have lost much of their importance. 



The work of Darwin embraces two main theses which as a rule 

 are not sufficiently distinguished and which even by him were fre- 

 quently collated. The one was to ascertain the common descent of 

 plants and animals, the other, to find how one species could have orig- 

 inated from another. These two points are mutually independent, 

 and were especially so at the time of publication of Darwin's 'Origin 

 of Species.' 



The doctrine of the common descent of all organisms holds that 

 genera, families and even the larger divisions of the plant- and animal- 

 kingdoms originated in a manner identical with the one which, before 

 the days of Linnaeus, was largely accepted for the splitting of genera 

 into species and afterwards for the formation of subspecies from spe- 

 cies. The common origin of groups of smaller types was recognized; 

 but how large these groups were no one knew exactly. Darwin ex- 

 tended their limits so as to enclose all living organisms, practically 

 collecting them into a single genus. 



For this purpose it was not even necessary to know how the simple 

 forms themselves originated. What was conceded for these by every 

 one, had only to be applied to the larger groups. Yet Darwin attached 

 considerable weight to this question and threw much light upon it. 



