EVOLUTION IN A DETERMINATE LINE AS ILLUS- 

 TRATED BY THE EGG-CASES OF 

 CHIM/EROID FISHES. 



BASHFORD DEAN. 



Recent attempts to explain evolutional processes, whether, 

 e - g-i by natural selection, orthogenesis or use-inheritance, have 

 been based, with but few exceptions, upon parent and offspring, 

 in the direct relation of one to the other. Thus, (i) in the newly 

 developed field of biometrics, variations in parent and offspring, 

 have been discussed in terms of precision ; (2) in embryology 

 and embryopathology, ingenious experiments have tested the 

 latent possibilities of the offspring at different stages in its career, 

 and (3) on the side of paleontology, variations of progeny and 

 parents have been examined on a giant scale in terms of survival 

 and obliteration of masses of individuals. On the other hand 

 observations are scanty, even in the present outburst of literature, 

 which test the relation of the young to its parents by indirect 

 means. This is, none the less, a line of inquiry which bids fair 

 to become a fruitful one. And we may even at the present time 

 consider what materials can be obtained which shall provide a 

 series of parallel changes between the offspring and, e. g., some 

 other product of the parent, and through such means furnish, as 

 it were, a point d'appui for evolutional studies. Thus : Are 

 there any means of ascertaining whether an animal in providing 

 for its progeny can produce structures ivhich form no organic part 

 of the young yet u'hich at the same time indicate accurately ivhat 

 the young unll need in the distant future. And if these structures 

 do occur, are they sometimes so special in their nature that they can- 

 not be interpreted as general provision for the embryo, but rather 

 for the late and complicated needs both of the genus for ivhich they 

 are provided and even of the species ? Obviously the parent has 

 physical continuity with its young, but has it more than this ? 

 Has it the power to anticipate accurately the needs of the 

 young, which it abandons and with whose subsequent fate it 



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