4 THE BUTTERFLIES OF NEW ENGLAND. 



moderately hea^y and tounli. It seems to be thinnest in the Vanessidi, 

 but the presenee of liigh thin ribs pre\ents one from readily examining 

 through the shell the nature of the contents or the condition of the embryo. 

 In the Pamphilidi, it is unusually thick and at the same time opaque, while 

 in some of the Lycaenidae, the walls of the cells are sometimes excessively 

 heavy, especially on the crown of the egg. 



The centre of the sunnnit is always occupied by the micropyle (Plates 

 (67-69), a system of delicate microsc(>[)ic canals, usually from four to six in 

 number, which radiate from a minute })it in the very centre, and the mis- 

 sion of which is to convey into the egg spermatic threads for its fertiliza- 

 tion. Around these is a rosette of minute cells, the character of which in 

 the Pamphilidi differs but little from ordinary cell structure exce[)ting in its 

 delicacy. In nearly all butterflies it occupies an inconsiderable portion of 

 the summit of the egg and in some species is either so minute or obscure 

 as with difficulty to be seen at all, excepting under the most favorable 

 light. Usually it is slightly depressed, and in some cases is situated at 

 the bottom of a profound pit, but in others the contour of the shell is 

 not disturbed by its presence. The cells generally increase in size from the 

 centre outward, and, although sometimes comparatively few in nmnber and 

 arranged, especially the central ones, in a definite pattern, are more com- 

 monly crowded rather confusedly together. 



Internal changes, as seen externally. 



Having been unable to improve my opportunities of studying the embry- 

 ology of butterflies, and almost nothing being known concerning the 

 changes they undergo within the egg, I am forced to content myself here 

 with bringing forward the following brief statements concerning such phe- 

 nomena as may be witnessed through the usually rather opaque shell. This 

 I the less regret as I have obtained the kind cooperation of Dr. Woodworth, 

 whose special study of the embryological history of Euvanessa antiopa 

 will appear in the closing section of this Introduction. 



The changes which transpire within the eggs of butterflies, as viewed 

 through the external envelope, may be said to indicate rudely four distinct 

 stages of development ; all of these stages, excepting perhaps the last at its 

 close, are often greatly or entirely obscured from view, either by the opacity 

 of the shell itself, as in some of the Pamphilidi, or by the confusion arising 

 from the rough sculpturing of the outer surface, as in the Lycaeninae, 

 Basilarchia, Pieris and the Argynnidi, and even to some extent in the more 

 delicately marked Vanessidi. 



In the Jir.st period the contents are homogeneous, just as when they are 

 laid, when only a pure color, shining through the integument, can be seen ; 

 this condition lasts but a short time, — doubtless nmch shorter than appears 

 from the indications which can penetrate the shell ; a certain change makes 



