18 BRITISH LEPIDOPTERA. 



often revealed by the structure of the larvae As the embryo 



often shows us, more or less plainly, the structure of the less modified 

 and ancient progenitor of the group, we can see why ancient and 

 extinct forms so often resemble, in their adult state, the embryos of 



existing species of the same classes Embryology rises greatly in 



interest, when we look at the embryo as a picture, more or less 

 obscured, of the progenitor, either in its adult or larval state, of all 

 the members of the same great class." 



We may now look briefly at the embryonic life of a lepidopterous 

 insect from the time of the fertilisation of the ovum, until the larva 

 hatches from the egg. This can only be done by the aid of a micro- 

 scope. A very simple instrument with two lenses, a f and , is 

 sufficient for ordinary purposes, although, of course, many other 

 accessories are exceedingly useful. 



To get eggs for this purpose, take an ordinary glass tube and 

 enclose a few females of some common Tortricid moth. These moths will 

 usually lay their eggs on the glass, and their eggshells are so trans- 

 parent that the changes may be readily observed. Among the butter- 

 flies, eggs of Pararge inegaera and Nemeobitis lucina are not at all unsuit- 

 able for observation. 



It is sometimes inconvenient to study the embryological changes 

 which go on in an egg under a microscope, at the time that they 

 actually occur. Two very good methods have been described in detail, 

 by which the eggs may be killed and preserved for future observation. 

 One of these is the distribution of the eggs in phials, one phial to be 

 filled with carbolic acid, an egg put in, and the phial stoppered on 

 each day, until the final one contains the newly-hatched larva. The 

 other is to kill by heating in water at 80 C., then puncture the eggs 

 with a fine needle, and stain with " Grenachar's borax carmine " or 

 " Czochar's cochineal." 



It is an established fact of science, that every living being is 

 evolved from a single unicellular germ. The egg in insects is not the 

 earliest condition of the creature, because the primitive ovule can be 

 traced back to the ovariole, or even to the primitive ovary, before the 

 ovariole is developed. There is no need here to enter into the 

 development of an ovum from the primitive ovary, as it is fully de- 

 scribed elsewhere. Suffice it to say, that the ovum at last is formed 

 in the egg-chamber, and consists of a mass of yelk surrounded and 

 embedded in protoplasm, and containing the female pronucleus, whilst 

 at the time that the egg is laid, the main mass of it is made up of 

 yelk-spherules. These spherules become granular, and the granules 

 gradually replace the spherules, and are themselves again changed 

 into yelk-cells, the probability being that they are thus changed in 

 order to form suitable nourishment for the young embryo. At this 

 time, the newly-formed blastoderm-cells begin to pass towards the 

 circumference, leaving the degenerated yelk-cells in the centre. In 

 addition to these yelk-spherules, the egg contains a homogeneous fluid, 

 which has the ordinary composition of protoplasm, and consists 

 essentially of the chemical elements, carbon, hydrogen, oxygen, nitro- 

 gen, sulphur, phosphorus, lime, soda, potash, and other substances in 

 minute proportions. The great characteristic of this protoplasmic 



* Entom. Record, vol. v., p. 212. 



