(0!^ AND ^^^^ 



JOURNAL OF VARIATION. 



No. 5. Vol. V. May 15th, 1894. 



I'lie Life-jJistopy of a Lepidopterous Iiisect, 



Gomprising some account of its Morphology and Physiology. 



By J. W. TUTT, F.E.S. 



(Continued from page 92). 



Chap. II. 

 THE OVUM OR EGG. 



1. On the external structure of the egg. — The egg of a 

 lepiclopterous insect consists of an outside shell, enclosing protoplasm 

 which is at first homogeneous. The outside shell, which forms a thin 

 pellicle, is usually divisible into a base, walls and an aj)ex, the latter 

 being termed the " micropyle." By its base, which is usually flat and 

 devoid of characteristic markings, the egg is attached to the surface of 

 the food-j^lant or other object on which it is deposited by the parent. 

 The walls are generally sculptured in some form or other, although they 

 are sometimes quite smooth. The micropyle, wliich is situated at the 

 summit of the egg, is composed of delicate microsco})ic canals ; these 

 vary in number but there are rarely less than four or more than six ; 

 they radiate from a small depression in the centre of the summit and 

 round this depression is a rosette or circle of tiny cells, which are 

 usually of gi'eat delicacy. The micropyle is always excessively 

 minute ; in some eggs, even when viewed under a powerful lens, no 

 alteration of the ordinary outline is caused by it ; in others, however, 

 where it is more depressed it is more readily distinguished. It is through 

 the canals of the micropyle that the sperm-cell of the male passes to 

 fertilise the egg. 



The number of longitudinal ribs running from the base to the 

 micropyle varies ; in the Vanes.- kli there may be as few as eight, whilst 

 among the Ithodoceridi, in the genus Eurema, there are, according to 

 Scudder, from thirty to forty. The space between the ribs is broken 

 up into fine reticulations which are due to the existence of transverse 

 ribs of a much more delicate nature than the longitudinal ones. These 

 latter, however, vary considerably, sometimes being coarse and at others 

 very delicate, sometimes so delicate indeed, that the surface of the egg 

 appears smooth until it is examined through a lens of high magnifying 



