46 



On the Ova of Lepidoptera. 



By Frederick Noad Clark. Read January loth, 1901. 



It will be perhaps as well at the commencement of my paper to 

 make a few remarks on the methods I have employed in photo- 

 graphing the eggs exhibited, and at the same time to express my 

 obligations to those gentlemen who have so kindly supplied me with 

 material, amongst whom are Dr. Chapman, Messrs. Tutt, Mont- 

 gomery, Carpenter, and R. M. Prideaux, of Reigate. To Mr. Tutt 

 i am especially indebted for notes on the application of oval struc- 

 ture to the principles of classification. 



In every case the eggs have been photographed at precisely the 

 same magnification, and thus a good idea of their relative size is 

 conveyed. Whenever possible they are represented as they were 

 laid on their natural support, food-plant, etc. ; but as it is most 

 important for correct definition that the eggs should be all in one 

 plane of focus, I have in several cases been obliged to detach them 

 from their support and place them on a flat surface having a white 

 or black background for contrast, according to the colour of the egg 

 in question. The larger spherical eggs for the same reason present 

 some difficulty in photographing. It is desirable to photograph the 

 egg as soon as possible after being laid, so as to avoid changes in shape 

 or colour, which occur sooner or later in most cases, and to obviate 

 which some efficient method of preserving lepidopterous ova as 

 permanent specimens is very much needed. 



I am unable through lack of specimens to show typical examples 

 of all the families, but hope to do so at some future time. 



So far as I am aware no theory except that of natural selection has 

 been advanced to account for the variation in structure of the egg. 



" The eggs of Lepidoptera are developed in the ovaries of the 

 female, and after passing down the oviduct into the vagina, are im- 

 pregnated or fertilised with the male element or spermatozoa which is 

 stored after copulation in one or more pouches called the recepta- 

 cula seminis. A single spermatozoid is sufficient for this purpose, 

 and enters the egg at an orifice called the micropyle. This is of 

 microscopic size, in some cases hardly perceptible, in others it con- 

 sists of a distinctly depressed area. Minute channels communicate 

 with the interior of the egg and convey thereto the fertilising 

 element. 



"The base of the egg is, strictly speaking, that portion opposite 

 the micropyle, but in those eggs that are laid on their sides the 

 term base is sometimes misapplied; as for instance when it is 

 described as that portion of the egg which is attached to its 

 support or food-plant. 



