THE OVUM OR EGG. 



9 



We have seen that certain families are characterised by their 

 species possessing a flat egg, and that others are characterised by their 

 species possessing an upright egg. The Lasiocampids have a flat egg, 

 yet the eggs of Erioyaster lanestris and Clisiocampa neustria and C'. 

 castrensis have the appearance of upright eggs, so far as their position 

 with regard to the twig on which they are laid is concerned. This, 

 however, is not really so, for the eggs are laid upon their long sides, 

 on each other. A case of precisely opposite character occurs among 

 the Noctuids, the eggs of Leucania littoralis being laid on their sides 

 upon (or against) each other, although theoretically, no doubt, they 

 may be assumed to be laid uprightly upon the edge of the fold of 

 the leaf, in which they are placed. 



There is considerable difference in the thickness of the eggshell of 

 various lepidopterous eggs. In many species, it is so thin that the 

 development of the embryo can be distinctly traced through it. The 

 eggs of Tortricids and Pyralids are specially remarkable for the thinness 

 of their shells ; but, even in the same super-family, there is consider- 

 able difference. Among the Papilionids, the shells of Vanessa io, of 

 Pararge and of Nemeobius, are very delicate ; those of the Lycaenids 

 and Pamphilids are particularly tough and opaque. The eggshells of 

 Leucania littoralis among the Noctuids, of GalUmorpha liera and 

 Euthemonia ritssula among the Arctiids, of all the species of the 

 Zygaenids, are all exceedingly delicate. 



When the egg is first laid, the outer pellicle is soft and yielding, 

 and, if it be disturbed ever so slightly, an impression is made in its 

 external appearance. In some cases, the egg, when first laid, is ex- 

 ceedingly soft, and looks as if it were almost fluid. Such eggs, laid on 

 glass, apply themselves to it, and have a very regular and almost 

 perfectly circular or oval outline ; but if laid on a leaf or other irregular 

 surface, they apply themselves to its irregularities, and become them- 

 selves irregular, both in relation to the surface to which they are 

 applied, and also as regards their disturbed outlines. Chapman refers 

 to the evident irregularity observable in eggs laid by Scopula decrepi- 

 talis on a Teucrium leaf. The base of the eggs of Colias sometimes 

 spread considerably ; the eggs of Gonepteryx rhamni are often flatter 

 on one side than the other. Eggs of Pieris and Eucldq'e also show a 

 basal flattening that would probably not occur if they were quite free. 

 The egg of Calliyenia miniata, which has a very Pierid appearance, 

 varies much in shape, some eggs being much stumpier than others. 

 The variation in the shape of the eggs of Tephrosia bistortata and T. 

 crepuscularia (biundularia), even when laid quite free, is considerable ; 

 whilst the eggs of these species, as well as those of Anchocelis litura, 

 A. instacina, Orrhodia vaccinii, 0. ligula, Dicijcla oo, and others, 

 pushed into crannies of bark, may sometimes become so altered by 

 the process, that the typical shape and ribbing are entirely lost. This 

 is the case also with the eggs of Leucania littoralis, which are laid, as 

 before noticed, in the folded edge of a leaf. In eggs of this descrip- 

 tion, it need hardly be said, the change in shape has no injurious 

 effect on the development of the embryo. 



There is, sometimes, considerable difference in the size of eggs, 

 even when laid by the same moth. Harwood has noticed differences 

 in the size of the eggs among the Notodonts, and is inclined to 

 associate the difference in size with a difference in sex, assuming that 



