RECAPITULATION. 509 



modified in correspondence with the uniformity or the 

 periodicity of the external conditions to which it is exposed, 

 and we can only infer that the influence of the external condi- 

 tions is the cause of the modifications. We have reason to 

 believe that in the individual the total absence of light leads 

 to a progressive deterioration of eyes, and if this progressive 

 change, repeated in every generation, ultimately becomes 

 hereditary, then it would begin earlier and proceed farther 

 in successive generations. On this view the very imperfect 

 and incomplete recapitulation which we actually observe is 

 the necessary consequence of the fact that the animals are 

 exposed throughout their ontogeny to complete darkness. 



LIST OF AUTHORITIES CITED. 



Adam Sedgwick. On the Law of Development, commonly known 

 as von Baer's Law, etc. Qimrt. Journ. Mic. Set., vol. xxxvi., 

 1894. 



E. W. Macbride. Sedgwick's Theory of the Embryonic Phase of 



Ontogeny as an Aid to Phylogenetic Theory. Quart. Journ. 

 Mic. Sd., vol. xxvii., 1894-95. 

 W. K. Parker. Structure and Development of Skull in Batrachia. 

 Pt. ii. -P/iiV. Trans., vol. clxvi., 1877. 



F. E. Beddard. Notes upon the Tadpole of Xcnopus laevis {Dacty- 



letJira capensis). Proc. Zool. Soc, Feb., 1894. 

 F. E. SCHULTZE. Ueber die Abwartsbiegung des Schwanztheiles 



des Wirbelsaiile bei Ichthyasauren, .S. B. d. Berl. Akad., 



1894. 

 Tr. Ahlborn. Ueber die Bedeutung der Heteroccrkie, etc, 



Zeitschr. f. zviss. Zool., Bd. Ixi. 

 Alex. Agassiz. Development of the Tail of Osseous Fishes. 



Proc. Amer. Acad. Arts and Set., vol. xiii., 1877. 

 GUSTAV Joseph. Ueber das Zusamentreffen von Lichtmangel, 



etc. Entojn. Monatsbldtter, Berlin, 1876. Sita. Ber. Sc/iles. 



Ges. in Breslau, Nov., 1875. 

 E. Zeller. Ueber die Fortpflanzung des Proteus anguineus 



und seine Larve. JaJiresb. ber. Naturk. Wiirtt., xlv., 



1889. 

 W. E. RiTTER. On the Eyes, the Integumentary Sense Papillae, 



etc., of the San Diego Blind Fish. Bull. Mus. Comp. Zool., 



Harvard, vol. xxiv., 1893. 



