﻿170 BLIND VERTEBRATES AND THEIR EYES. 



the eye also tend to locate the formative or hereditary power in the cartilages them- 

 selves rather than in the stimuli to their develojiment that they receive from their 

 contact with the developing eyes, for they develop entirely l)eyond the needs of these 

 eyes.' 



The causes operating in ontogeny anfl phylogeny that have led to the limited 

 power of development and differentiation I have fully considered in the concluding 

 chapter, which was also published in the Popular Science Monthly.- The conclu- 

 sion is reached that the phylogenetic degeneration, which is equivalent to saying the 

 limited power of development found in the cells entering into the eye of the indi- 

 vidual, is the result of functional adaptation during the lifetime of past individuals 

 to the total disuse of the eye. This adaptation, it was concluded, was transmitted 

 to a certain extent to the succeeding generation through the usual vehicles of trans- 

 mission. There has always been and is yet a sericnis objection to this conclusion, 

 because the method of the transmission of functional adaptations to the organiza- 

 tion of the egg so as to limit or extend its powers is not known. 



Recently, while admitting that functionally adaptive structures arise develop- 

 mentally without reference to function, Driesch has maintained that: "Wer hicr 

 von 'Vererbung' friiher einmal functional 'erworbener' Eigenschaften reden will 

 verlasst den wissenschaftlichen Boden, denn wir wissen von solcher Art der Verer- 

 bung gar nichts." 



Possibly we miglit lind a warrant for the assumption of the transmission of func- 

 tional adaptation to the germ cells in the writings of Driesch himself, though he 

 might not thank us for it. He maintains that certain developmental results whose 

 proximal cause he is not able to determine may be produced by factors working in a 

 distant part of the embryo. Without entering into a discussion of the validity of 

 these factors working at a distance, if they are really factors and capable of acting, 

 as Driesch imagines, why may not functional modifications effect changes in the 

 hereditary cells in a similar manner ? 



I conclude that retardation and cessation in deveIo]:)ment are not due to onto- 

 genetically operating causes, but they are inherent in the fertilized ovum — they 

 are inherited. 



THE EYES OF AMBLYOPSIS AND THE LAW OF BIOGENESIS. 



During recent years the law variously termed von Baer's law, Agassiz's law, 

 Haeckel's law, or the law of biogenesis, has been frequently called into question. Its 

 general tenets are : (i) every individual in its development repeats in brief the devel- 

 opment of the race ; (2) closely related forms have a similar ontogeny, and the nearer 

 two animals are related the longer their embryos are alike ; (3) tlie embryos of high 

 animals pass through stages resembling the ackilt stages of lower animals ; and 

 (4) in every ontogeny there are, among the truly ancestral stages, stages which are 

 adaptive and have been acquired during ontogenetic development. 



No objection has been raised to the fourth tenet in so far as its acceptance does 

 not commit to the accei)tance of the first. In objection to the first of these proposi- 

 tions Hurst writes : 



I do not deny that a rough parallelism exists in some cases between ontogeny and phylogeny. 

 I do deny that the phylogeny can so control the ontogeny as to make the latter into a record of the 



' The same conditions are found in Lucifuga. ' See the next chapter. 



