to a small gate or opening, through which the worm is seen to emerge forth. From a number of observations made on silkworms' eggs, I have not been able to satisfy myself of the correctness of the particulars described by this observer, nor have I seen the young worm make its way out at this precise spot, but generally at a point much below it. Leuckart states this depression, the micropyle, becomes at a certain period converted into a funnel, which is directly connected with the mouth of the embryo, and serves to convey nourishment from without to it. I see no grounds for such a statement; because in the silkworm's egg, instead of a depression at this point, we have a nipple, and there can be no more necessity for leaving this funnel-shaped opening for the nourishment of the embryo catterpillar, than for that of the chick. There is no opening for such a purpose in the ovum of the bird; indeed the vitelline membrame appears to form a perfectly closed sac to the yolk. In some eggs we appear to have an involuted portion of membrane, indicating simply where either the formative process of the outer membrane terminated, or the spermatozoa passed in to fecundate the yolk mass.*

The germinal vesicle is situated in the yolk mass, it is well marked, and of a very large size, in the egg of the bee, while the egg is yet in the ovasac. By preparing sections, after Dr. Hallifax's method, I find that the germinal vesicle of this insect is not situated immediately near, nor even below, the so-called micropyle, but more to the side of the yolk, represented in Fig. 17, and just in the position which the head of the embryo is found subsequently to occupy towards the end of the period of incubation. The germinal vesicle is well marked; its macula is at first single, then becomes multiple.

The egg membrane, or shell as it is incorrectly called, of the moth and butterfly, is composed of three separate layers; an external slightly raised coat, tough and hard in its character; a middle one of united non-nucleated cells; and an inner one clear, dense, and homogeneous in structure, imparting a fine iridescent glaze to the surface, such as we see and admire in the old glass vessels exhumed from the ruins of Pompeii.

In the silkworm's egg the outer membrane consists of an inner reticulated membrane of non-nucleated cells, and an outer layer, the cells of which are arranged in an irregular circular manner, also non-nucleated, with a number of minute projecting interstitial hairs, or setæ. This layer has probably

"As to the origin of the micropyle, it does not appear to proceed, as has been supposed by Meissner, from the mere deficiency of the epithelium cells in a certain space, and it is not dependent, either, on its pre-existence in the vitelline membrane, but, according to Leuckart, it is found in the chorion before it appears in the vitelline membrane."-DR. ALLEN THOMSON.

served, at some time, while the egg was yet a part of the ovarium ovum, as a vascular coat, and being no longer required, has become consolidated to form a part of the dense membranaceous covering.

It is in these several layers of the outer membrane that the micropyle apparatus is situated, and it should be noted that Meissner has described several varieties of the micropyle in the ova of insects belonging to the following genera, viz., muscœ, tipula, pulex, lampyris, elater, teleophorus, adela, pyralida, tortrix, euprepia, liparis, pieris, panorpa, and in more than one species of several of these genera. The same author also observed and described in Musca vomitoria, a number of spermatic filaments entangled in the micropyle. Leuckart's observations, which are apparently more complete than those of Meissner, differ from his in some particulars; they extend over several hundreds of different kinds of insects' eggs, and he asserts that he succeeded in detecting the existence of the micropyle in not less than 200: he also gives detailed observations on this apparatus, and the structure of the membranes. I willingly admit that such an extended series of observations fully entitles this author to great respect; and when we consider the minuteness of the eggs, and the difficulty of obtaining specimens in a suitable condition for investigations of the kind, we may appreciate the importance of the work, and the amount of labour required to bring such an investigation to a satisfactory conclusion. Leuckart positively asserts that, "in all instances in which the ova were ripe and favourable for examination, he was enabled to assure himself of the presence of the micropyle." This supposed opening will be readily recognised in many of the drawings accompanying this paper, forming, as it does, a prominent spot at the pole of the egg, or in the middle of the circular radiants in the lid.

The outer surface of the egg shell of Coccus Persica is covered by a series of minute rings, the ends of which somewhat overlap. These rings are believed by Sir John Lubbock to be identical in their character with the whitish substance which exudes through pores on the underside of the body; and it is more than probable that these layers of rings, and their arrangement, account for the beautiful prismatic hues which the egg presents under the microscope, when viewed as opaque objects. This substance, it appears, ultimately becomes a part of the intimate structure of the egg membranes. With regard to the greenish colour of the eggs of Phryganea, the same observer states "that it is due to the yolk-globules themselves.* In Coccus this is not the case, the yolk-globules are slightly yellow, and the green hue of the egg is owing to *Phil. Trans. 1859, p. 341.

the green granules, which are only minute oil globules. When, however, the egg arrives at maturity, and the upper chamber has been removed by absorption, these green granules will be found to be replaced by dark green globules, regular in size, and about 1-8000th of an inch in diameter, and which appear to be in no way the same in the yolk of Phryganea egge." Another curious fact has been noticed, which partially bears on the question of colour, the production of parasitic bodies within the eggs of some insects. In the Coccus, for instance, parasitic cells of a green colour occur, shaped like a string of sausages, in length about the 1-2000th of an inch, by about the 1-7000th of an inch in breadth. Of the formative process and composition of the colouring matter, not much is known. Valenciennes and Framy, after having bestowed attention on this part of the investigation, selecting the ova of Crustaceans for their purpose, arrived at the conclusion "that it is the same as that existing in the shell; which being green in the moist state, passes into a red colour when solidified." By the aid of alcohol, etc., the colouring matter can be separated and collected in sufficient quantities for spectrum examination. The eggs of moths and butterflies, as I have before stated, present many varying tints of colour, and in speaking of this quality I do not restrict the term solely to the prismatic changes to which allusion has been made, and which are liable to constant mutations, according to the accident of the rays of light thrown upon them, but I more particularly refer to the several natural transitions of colour, the prevailing tints of which are yellow, white, grey, and a light brown. In some eggs the yellow, white, and grey are delicately blended; and these, when viewed with a magnifying power of about fifty diameters, and by the aid of a side-reflector (parabolic reflector), present many beautiful combinations, and the most delicate opalescent, or rather iridescent tints appear on others. The egg of the Mottledumber moth (Erannis defoliaria), Fig. 8, is in every particular very beautiful. It is ovoid, with regular hexagonal reticulations, each corner is studded with a white raised knob or button; the space within the hexagon is finely punctuated, and the play of colours is exquisitely delicate. In this egg I have been unable to make out a micropyle. The Magpie moth (Abraxas grossularia), Fig. 1, is another example. The egg is ovoid, and somewhat resembles the former, but does not possess the raised stud or button, at the corner of each hexagon; its colour is very delicate, and silvery in tone. The membrane is so translucent that the movements of the young worm can be very well seen within. The egg of the Thorn moth (Ennomos erosaria), Fig. 5, is an elongated square form, one end of which is slightly tapered off, while the other is flattened; in this

the lid is placed, surrounded by a beautifully white-beaded border, having in its slightly raised reticulated centre the micropyle. The empty egg-shell gives a fine opalescent play of colours, while that containing the young worm appears of a brownish yellow colour. The egg of the Straw-belle moth (Aspilates gilvaria), Fig. 2, is very delicately tinted; it is somewhat long and narrow in form, with sides slightly flattened or rounded off, and is regularly serrated. The top is convex, and the base a little indented; in the latter is seen the lid and micropyle. The young worm, however, usually makes its way through the upper convex side; the indentation represented in the drawing shows the place of exit. One belonging to a very interesting class of moths, the Dingy-shears (Exarnis ypsilon), is shown in Fig. 3. A small sub-conical egg, with a flattened base, which admits of its being firmly cemented to either bark or leaf. The egg is beautifully reticulated, the ribs are slightly raised from the membrane, and connected with each other by cross-bars; they run from a marginal ring surrounding the micropyle, in regular order to the base, and a series of fine lines radiates from the central spot to the border.

An example of those eggs possessing a good deal of natural colour is shown in Fig. 10. The Puss moth (Cerura vinula), a large spheroidal shaped egg, having, under the microscope, the appearance of a fine ripe orange; the micropyle exactly corresponds to the depression left in this fruit by the removal of the stalk. The surface of the egg is finely reticulated, or rather has the appearance of a piece of netting stretched tightly over it. The colour is a deep orange. The egg of the Swallow-prominent (Pheosia dictæa), Fig. 4, is in shape and size nearly the same as the former. It is spheroidal, slightly flattened at the poles, and, with the exception of one spot, that of the micropyle, the surface is a continued series of regular indentations, reminding one of those fine reticulations, or markings, seen on some of the Guiano shells. The colour is a very delicate pink. There are others rather more decided in their colour, as the egg of the Brimstone moth (Rumia cralagata), remarkable for its hexagonal reticulations, it is yellow, spotted with red; that of the Lappet moth (Gastropacha quercifolia), with its bluish colour, and three circular bands of brown. The Buff-tiger moth (Diacrisia russula), Fig. 7, lays an exquisite little globular egg, the external membrane of which is covered by a fine network of irregular hexagons, which terminate at the pole in a micropyle. It has all the appearance of an iridescent minute glass globule, and is so translucent that the young worm can be seen through it. The Browntail moth (Euproctis chrysorrhea), Fig. 12, produces a small spheroidal egg, which, slightly flattened at the poles, is

uniformly covered with imbricated scales, and is terminated in the upper pole by a geometrical series, which fold in towards the micropyle. In every instance the worm eats its way out of the side of the egg; the aperture is shown in the drawing; this moth appears to cover her eggs with fine hairs, and the empty spherical egg cases are beautifully iridescent. The egg of the small Emerald Volute moth (Jodis vernaria), Fig. 16, is remarkable in form, which is somewhat oval, but flattened on the broad side, of silvery whiteness, covered with minute reticulations and dots, peculiarly translucent, so much so that the little yellow-brown worm is seen curled up within, as shown in the egg to the left. At first it appears difficult to detect the presence of either lid or micropyle, and it is not until after the worm has eaten its way out that you clearly see at which end it was placed. The aperture through which it has made its escape is shown in the egg to the right. As to the change of colour (which occurs from physiological causes), connected with the development of the embryo, a remarkable instance is afforded, and one from which the insect partly derives its name, in the Glory of Kent (Endromus versicolor). The egg is first bright yellow, then successively green, rose colour, and reddish black. A still more familiar instance is presented in the egg of the Silkworm moth (Bombyx mori), Fig. 11, which when first laid is of a delicate pale yellow, this hue it retains for some time, it is subsequently of a reddish brown, and just before the embryo quits the egg it acquires a slate colour, partaking for the time being of the colour of the embryo within; but so soon as the worm emerges forth, the shell regains its original pale yellow. The micropyle, if that can be so called, which in this egg is a raised nipple, is in the more flattened pole of the egg. The mouth of the young worm lies towards the horn of the crescent of that pole, and it is at this point the first cut is made, just sufficient of the membrane is eaten away to admit of the head and body passing through the aperture. The outer and inner portions of the egg membrane are represented magnified 150 diameters at a and b, Fig. 11.

The egg of the small Silver-lines moth (Hylophila prasinana), Fig 9, is yellow brown, in form a truncated pyramid. The micropyle is enclosed in a regular series of radiating lines. A series of raised ribs are set in regular order around the sides, and the cross bars which connect them. These present a pretty basket-like pattern. The egg is flattened out at the base, apparently for the purpose of securing it more firmly to the leaf. The Meadow-brown butterfly (Epinephile janira), Fig. 14, lays a sub-conical egg, considerably flattened towards the apex, the raised ribs which stand away from the sides have a silvery colour, and give to the whole a corrugated appearance.