174 HUBERT DANA GOODALE 



INTRODUCTION 



Early in May, 1904, while searching for the eggs of Plethodon 

 cinereus, then unknown to me, I found a single batch of white 

 eggs in early cleavage stages attached to the under side of a stone 

 taken from a brook. Later, when the eggs were found in great 

 abundance, they were identified as those of Spelerpes bilineatus. 

 Search of the literature showed that only the later stages had been 

 described in a brief paper by Wilder in 1899. According to 

 Wilder, the eggs were not well known, having been recorded by 

 Verrill only. 



I was encouraged by Professor Charles L. Edwards of Trinity 

 College to undertake the study of the development of these eggs. 

 I desire to express my appreciation of this encouragement and 

 to thank him for the use of the Biological Laboratory during the 

 spring of 1905. Since the fall of 1904, the work has been carried 

 on at Columbia University under the direction of Professor T. H. 

 Morgan, to whom my best thanks are due for much kindly advice 

 and criticism. 



The experimental part of the work was undertaken by means 

 of an entirely new method. It has proved possible to produce 

 artificial spots of color in the living egg and thus follow out the 

 shiftings of material in the normal egg, which hitherto has been 

 done only by puncturing the egg. The results entirely confirm 

 those obtained by the latter method, thus removing the objections 

 of those who, like Ikeda, believe that results obtained from 

 injured eggs are inapplicable to the normal egg. 



PART 1. DESCRIPTIVE 



The egg and its envelopes 



The diameter of the egg varies from 2.2 to 3 mm. The upper 

 hemisphere of the egg is snowy white but the lower has a faint 

 yellowish tone. It is enclosed in several envelopes, shown in 

 optical section in fig. 1. The delicate outer layer, a, is thin and 

 difficult to make out except at the point of attachment, a.' The 

 inner surface, c, of the next layer, b, is tougher than the remainder 

 since the latter is easily removed. The perivitelline space, d, 



