41 6 THE POPULAR SCIENCE MONTHLY, 



in so much greater as the Invertebrata, with perhaps the exception of 

 the Articuhita and the Radiata, are less pronouncedly typical and 

 physiologically less intelligible. 



This uncertainty of the laws of organic structure comes from the 

 fact that these laws themselves are purely experimental, containing in 

 themselves no ultimate, logically cogent truth such as we find in physico- 

 mathematical laws. Hence, a departure of nature from these rules im- 

 plies no contradiction, no impossibility ; and if a thing is not impossible, 

 of course it is possible. 



Physico-mathematical laws form, as it were, a resting-place on which 

 we may safely step without fearing that it will ever fail under our 

 weight. In the history of development, on the other hand, what has 

 been our experience ? Within a short period of time, a very restricted 

 survey of the animal world, a survey guided by chance, made us ac- 

 quainted with a series of facts that conflict with all our previous knowl- 

 edge. Discoveries like that of the inverted position of the embryo in 

 'certain rodents, of the development in the deer, of alternate gen- 

 erations, of the development of the echinoderms, of the Entocoiicha 

 mirabUis, of parthenogenesis, of hectocotjly — all these are calculated 

 to put us on our guard against premature generalization in this field. 

 But in fact such anomalies as these are only counterparts of others with 

 which we have long been familiar, as the marsupials, viviparous fishes, 

 etc., which make no impression on us, because already known to science. 



Under such circumstances the application of the biogenetic funda- 

 mental law to individual cases is very hazardous, even though we admit 

 the principle in a general sense. The inferences which ontogeny, 

 guided by a few scattered paleontological characters, permits us to draw 

 with regard to phylogeny, will never possess more than a very restrict- 

 ed degree of probability. It will ever be open to the individual under- 

 standing to take whatever way it chooses amid the confusion of innu- 

 merable and complex possibilities, and, excepting a few indisputable 

 points, which, however, were understood long ago, to conceive a great 

 many diff'erent modes of development of the organic world as it exists 

 now. As for certain genealogies of our race drawn up in unfettered 

 presumptuousness rather by an artistic imagination than by a scientifi- 

 cally trained mind, they are of about the same value as the pedigrees 

 of Homeric heroes in the eyes of the histoi'ical critic. For my part, if 

 I want to read a w^ork of fiction, I can find something better than a 

 *' History of Creation." 



But this is not the point which concerns us just now. Granting the 

 scheme of descent from the little mass of protoplasm with which 

 life is supposed to have begun, up to man himself, to be clearly made 

 out (which it is not), the fashioning of organic nature will, after all, be 

 as great a riddle as ever, if laws of structure have alone determined its 

 development. 



And this, not because molecular mechanics, which produces modifi- 



