NATURAL SCIENCES OF PHILADELPHIA. 239 



I think that I have already made some progress in proving that the near or 

 true generic relationship is one of absolute developmental repression or 

 advance. Paleontology shows that families and orders, as now existing, were 

 preceded in time by groups which are synthetic or comprehensive, combining 

 the common characters of modern generic series. This process of synthesis 

 must, it is obvious, if continued, result in the near approximation of the single 

 representatives of the now numerous and diverse groups There is every reason 

 to believe that a baclvward view tlirough time will show this to have prevailed 

 throughout the vertebrata and other branches, as we already can in part jjrove. 

 And I have no doubt that the synthetic tj'pes. which represent modern orders, 

 have existed in a generic relationship subordinate to the plan of the synthetic 

 class, and that the latter have existed as genera only, of the type of the great 

 branch. This is not ideal. We only have to look to our extinct ganoids, 

 Archegosaurs, Labyrinthodonts, Compsognathus, Archaiopteryx, Ornitho- 

 rhynchus, etc., to realize these facts. 



The first genera then formed a scale of which the members were identical 

 with the undeveloped stages of the highest, and each to each according to 

 their position. 



Such a series of antitypic groups having been thus established, our present 

 knowledge will only permit us to suppose that the resulting and now existing 

 kingdoms and classes of animals and plants were conceived by the Creator 

 according to a plan of his own, according to his pleasure. That directions or 

 lines of development towards these ends were ordained, and certain laws ap- 

 plied for their realization. That these laws are the before-mentioned law of 



RETAKDATION AND ACCELERATION ; and law of NATURAL SELECTION. 



The first consists in a continual crowding backwards of the successive steps 

 of individual development, so that the period of reproduction, while occurring 

 periodically with the change of the year, falls later and later in the life his- 

 tory of the species, conferring upon its offspring features in advance of those 

 possessed by its predecessors, in the line already laid down partly by a 

 prior suppression on a higher platform, and partly as above supposed, by 

 the special creative plan. This progressive crowding back of stages is not, 

 however, supposed to have progressed regularly. On the contrary, in the de- 

 velo[)ment of all animals there are well-known periods when the most impor- 

 tant transitions are accomplished in an incredibly short space of time, (as the 

 passage of man. through the stages of the aorta bows, and the production of 

 limbs in Batrachia Anura;) while other transitions occupy long periods, and 

 apparently little progress is made. 



The rapid change is called metamorphosis ; the intervening stages may be 

 called larval or pupal. The most familiar examples are those which come 

 latest in life, and hence are most easily observed, as in the insects and frogs. 

 When, during the substationai-y period, the species reproduces, a constancy 

 of type is the result; when the metamorphosis only appears at the period of 

 reproduction a protean type is the result ; when the raeiamorphosis is crowded 

 back to an earlier period of life, then we have another persistent type, but a 

 new genus of a higher grade than its predecessor. 



In reviewing many examples everywhere coming under the eye of the natu- 

 ralist, it is easy to perceive what would constitute a plastic and what a con- 

 served condition of generic, or even of specific form. 



As one or more periods in the life of every species is characterized by a 

 greater rapidity of development (or metamorphosis) than the remaimler, so in 

 proportion to the apj)roximation of such a period to the ejioch of maturity or 

 reproduction, is the offspring liable to variation. During the periods corres- 

 ponding to those between the rapid metamori)hoses the characters of the genus 

 ■would be preserved unaltered, though the period of change would be ever 

 approaching. 



Hence the transformation of genera may have been ra])id and abrupt, and 

 the intervening periods of persistency very long; for it is ever true that the 



1868.] 



