NATURAL SCIENCES OF PHILADELPHIA. 243 



III. Relations of higher groups. 



rt. Of homologous groups. 



p. Of heterology. 



•y. Of mimetic analogj\ 

 lY. Of natural selection.* 



a. As affecting class and ordinal characters. 



0. As affecting family characters. 



y. As affecting generic characters. 



ef. As affecting specific characters. 



6. On metaphysical species. 

 v.. Of epochal relations. 



The laws which have regulated the successive creation of organic beings 

 will be found to be of two kinds, as it appears to the writer. The first, that 

 which has impelled matter to produce numberless ultimate types from com- 

 mon origins ; second, that which expresses the mode or manner in which this 

 first law has executed its course, from its commencement to its determined 

 end, iu the many cases before us. 



That a descent, with modifications, has progressed from the beginning of 

 the creation, is exceedingly probable. The best enumerations of facts and 

 arguments in its favor are those of Darwin, as given in his various important 

 works. The Origin of Species, etc. There are, however, some views respect- 

 ing the laws of development on which he does not dwell, and which it is pro- 

 posed here to point out.* 



In the first place, it is an undoubted fact that the origin of genera is a more 

 distinct subject from the origin of species than has been supposed. 



A descent with modification involves continuous series of organic types 

 through one or many geologic ages, and the co-existence of such parts of such 

 various series at one time as the law of mutual adaptation may permit. 



These series, as now found, are of two kinds ; the uninterrupted line of 

 specific, and the same uninterrupted line of generic characters. These are 

 independent of each other, and have not, it appears to the writer, been de- 

 veloped pari passu. As a general law it is proposed to render highly proba- 

 ble that the same specific form has elisted through a succession of genera, and 

 perhaps in ditterent epochs of geologic time. 



With regard to the first law of development, as above proposed, no one has 

 found means of discovering it, and perhaps no one ever will. It would 

 answer such questions as this. What necessary coincidence of forces has 

 resulted in the terminus of the series of fishes in the perches as its inost 

 specialized extreme; or, of the Batrachia, in the fresh-water frogs, as its ulti- 

 mum ; or, of the thrushes, among birds, as their highest extreme : in a word, 

 what necessity resulted in man as the crown of the Mammalian series, instead of 

 some other organic type ? Our only answer and law for these questions must 

 be, the will of the Creator. 



The second law, of modes and means, has been represented to be that of 

 natural selection by Darwin. This is, in brief, that the will of the animal, ap- 

 plied to its body, in the search for means of subsistence and protection from 

 injuries, gradually produces those features which are evidently adaptive in 

 their nature. That, in addition, a disposition to a general variation on the 

 part of species has been met by the greater or less adaptation of the results of 

 such variation to the varying necessities of their respective situations. That 

 the result of such conflict has been the extinction of those types that are not 

 adapted to their immediate or changed conditions, and the preservation of 

 those that are. 



In determining those characters of plants and animals, which constitute them 

 what they are, we have, among others of higher import, those which constitute 

 them species and those which constitute them genera. What we propose is : 

 that of the latter, comparatively very few in the whole range of animals and 



1868.] 



