762 



The American Naturalist. 



[September, 



a controversy with Reichert, over the existeDce of a vitelliDe membrane 

 on the surface of the egg. 



Similar wrinkles have since been observed in the eggs of the common 

 toad by Goette (Die Entwickelungsgeschichte der Unke), and of Am- 

 blystoma punctatum by Eycleshymer (Journal of Morphology, Vol X). 

 But neither of these authors offer any explanation of their origin, 

 far as known this Falteukranz " has never been described for any 

 American species of frog, nor has any attempt been made to study it 

 by means of serial sections. 



The following paper is offered as a contribution of some new and in- 

 teresting details in the occurrence of the phenomenon, together with 

 the results of a microscopic study of sections, in the hope of arriving at 

 a rational conclusion as to its origin. 



The author desires to acknowledge his great indebtedness to Dr. E. 

 A. Andrews, for the suggestion which led to the study, and for much 

 subsequent assistance. Thanks are also due to Prof. T. H. Morgan, for 

 the kindly loan of a copy of Schultze's paper. 



FORMATION OF THE WRINKLES. 



The eggs of a small wood-frog, in all probability Chorophilus triseri- 

 atus, were obtained for class work on March 27, 1896. 



They were unsegmented when found, and were immediately placed 

 in ice water to check any further development. 



After remaining thus for five hours they were used in the laboratory, 

 being removed to watch-glasses containing tepid water. Some were 

 allowed to remain in the ice water for eight hours before being exam- 

 ined, and it was noticed that these segmented much more rapidly than 

 the ones which had been kept only five hours. Actual segmentation 

 had been prevented during the stay in the ice water, but there seemed to 

 have been a storing-up of energy, a sort of preparation for segmenta- 

 tion, so that when removed to a favorable environment the process 

 began very quickly (5-10 mins.) and was carried on much faster than 

 it would have been normally. 



These eggs were obtained from pools covered with ice quarter of an 

 inch thick, and most of the bunches were quite near the surface. 



This must occur frequently where the eggs are laid so early in the 

 rspring ; and according to Morgan (American Naturalist, August, 

 1891), Chorophilus always lays its eggs very early. 



The storage of energy noticed above may suggest a natural method 

 of compensation whereby the warm sunshine of mid-day may offset the 

 freezing cold of the nights, and in this way the eggs will really lose 

 very little time in their development. 



