1»93.] ^^''J [Ryder. 



On the Development of the Cetacea, etc., A.nn. Rep. U. S. Com. of 

 Fish and Fisheries for 1885, pp. 427-485, PI. iii, 1887. 

 ' A Physiological Theory of the Calcification of the Skeleton, Proc. Am. 

 Philos. Society, xxvi, 1889, p. 9. 



The Polar Difierentiaiion of Volvox, etc.. Am. Naturalist, 1889, pp. 

 218-221. 



The Quadrate Placenta of Sciurus Jiudsofiius, Am. Naturalist, ]889, 

 pp. 271-274. 



The Origin of Sex, etc., Proc. Am. Philos. Society, xxviii, 1890, pp. 

 109-159. 



The Placentation of the Hedgehog and Phylogeny of the Placenta, 

 Am. Naturalist, 1890, pp. 376-378. 



A Geometrical Representation of the Relative Intensity of the Conflict 

 Between Organisms, Am. Naturalist, 1892, pp. 923-929. 



On the Mechanical Genesis of the Scales of Fishes, Proc. Acad. Nat. 

 Sciences, Philadelphia, 1892, pp. 219-224. 



The Principle of the Conservation of Energy in Biological Evolution ; 

 A Reclamation and Critique, Proc. Acad. Nat. Sciences, Philadelphia, 

 1892, pp. 455-468. 



The Inheritance of Modifications Due to Disturbances of the Early 

 Stages of Development, Especially in the Japanese Domesticated Races of 

 Gold-carp, Proc. Acad. Nat. Sciences, Philadelphia, 1893, pp. 75-94. 



The Mechanical Genesis of the Form of the Fowl's Egg. 



By John A. Ryder. 



(Read before the American Philosophical Society, April 21, 1S93.) 



The configuration of the outline of the hen's egg is determined appar- 

 ently by mechanical means while the egg-membranes and shell are in 

 process of formation within the oviduct. 



The conditions, after the passage of the ovum or yolk proper into the 

 oviduct, seem to he about as follows : 



1. In the upper part of the oviduct the albumen is laid down upon the 

 yolk by the activity of the albumen-secreting structures forming the wall 

 of the duct. This albumen is laid down in successive layers, as is proved 

 by the structure of the albumen and chalazse, when these are coagulated 

 by heat and then cut into thin sections. This lamination of the albumen is a 

 result of the mechanical relations that the yolk sustains to the surrounding 

 albumen-secreting surfaces, and this structure of the albumen is mechan- 

 ically caused. The chalazae are produced as the first deposits of albumen 

 in the oviduct behind and in advance of the yolk. The twisting of the 

 chalazffi is mechanically caused fur the reason that the twist of the chalaza 



