34 



HA RD WICKE 'S S CIENCE- G O SSI P. 



granules were aggregated in spherular masses, which 

 again were arranged in two groups : an annular 

 larger mass having a clear space outside between it 

 and the shell, and a clear central area in which the 

 smaller mass lay in an irregularly curved spiral or 

 crescentic form. For the sake of convenience, I shall 

 call these two masses of [opaque yolk the Annulus 

 and the Spiral. The former was composed of yolk- 

 spherules (i.e. aggregated masses of yolk-granules), 

 arranged, somewhat loosely at first, but by degrees 

 more compactly, so as to flatten their sides and give 

 them a polygonal form, in a flat oval ring, having the 

 same contour as the egg itself, but gradually wider at 

 one end than the other, not unlike a horse-collar. 

 The broader end was at first in all cases (except, 

 perhaps, N.W.) towards the south end of the egg.* 

 It maintained its shape with little change, except 

 some diminution in width and increase in density, 

 all the time that the eggs were under observation, i.e. 

 till the 9th August, when they were unfortunately 

 destroyed by an accident a day or two before 

 hatching would have taken place. The spiral, on 

 -the contrary, was constantly undergoing change, 

 and it soon became evident that its convex border 

 was the true seat of development. Regarded as a 

 mass of unchanged yolk, it had, on the 5th August, 

 somewhat the appearance of a double scroll (Fig. 32), 

 something like the capital of an Ionic pillar, and 

 with a stalk between roughly corresponding to the 

 shaft of the pillar, or, at least, the upper end of it. 

 The volutes of this scroll or double spiral were not 

 similar. One was sharp, dark and well defined ; 

 the other vague and changing, and made up of looser 

 granules of yolk. In all cases the sharper well- 

 defined volute lay towards the north. The stalk or 

 shaft between the volutes pointed in a general direc- 

 tion east or west, and after some hours became more 

 slender and formed an attachment with the annulus 

 on the inside. At this time the scroll was not unlike 

 the vertebrate embryo in an early stage with its 

 umbilical stalk, and, as no doubt yolk granules passed 

 into the embryo by this channel, there may have 

 been something functional in the resemblance as 

 well. 



To explain this annular arrangement of the food- 

 yolk it is necessary to refer to the formation of the 

 amnion. After the yolk has become surrounded by 

 the growth of cells called the blastoderm, and after 

 the germinal stripe, or foundation of the embryo, 

 has been differentiated along one side of this blasto- 

 derm, a double fold of the latter grows up all round 

 the circumference of the germinal stripe and finally 

 closes in over it, the edges of the fold fusing together 

 and the two layers (of blastoderm) of which it is 

 composed at the same time , separating from one 



* Under date August 7th, I have the following note. "In 

 the three northern eggs it is the northern half which is widest 

 now — in the three southern, the southern half, and more dis- 

 tinctly so." 



another. The inner of these, continuous with the 

 embryo itself, and lying immediately over it, is the 

 amnion ; the outer, continuous with the blastoderm 

 surrounding the yolk, is the serous membrane. Two 

 sacs are thus formed, the one within the other, and 

 between them lies the yolk. In the lepidopterous 

 egg the yolk next finds its way into the space 

 between the amnion and the serous membrane, flow- 

 ing over the former, and depressing it and the 

 embryo beneath it till both are completely submerged 

 in yolk and consequently hidden from view. But 

 owing to the extreme flatness of the Botys 1 eggs, little 

 or no yolk finds its way to the sides of the embryo, 

 but is constrained to lie in a ring around it, leaving 

 the centre clear, except that part immediately 

 beneath the germinal stripe, which by the involution 

 of the two extremities of the embryo becomes soon 

 reduced to a narrow capitate peduncle, the " umbilical 

 stalk," &c. (Fig. 33). 



A glance at the diagrams (Figs. 30 and 31), will 

 show that the umbilicus did not lie uniformly in 

 one direction east or west. When it had its 

 attachment to the annulus on the west, this meant 

 that the venter of the embryo was facing east, and 

 that (having its head south) it was lying on its right 

 side or with its right side next the glass : and vice 

 versd. This arrangement may be very well imitated 

 with the half-pence by placing them upside-down, 

 and with the queen's head up to represent the embryo 

 on its right side, and the figure of Britannia up to 

 represent it lying on its left side with the venter 

 looking west. The only thing to be noted in this 

 connection (and the small number of the total 

 observations makes it the less reliable), is that in 

 both* groups of eggs all the lateral eggs, i.e. those 

 not situated on the central axis or meridian of the 

 group, had their umbilici directed towards the 

 meridian, and their ventres consequently looking 

 outwards. To this statement there were two excep- 

 tions in the group of nine ; viz. N.W., which did not 

 develop at all, and N.E., which had its venter looking 

 inwards, but failed to hatch out. 



There was a considerable difference in the rate of 

 development of the different eggs in the group of 

 seven. S.W. appeared to be the most advanced, 

 although latterly N.E. was not much if anything 

 behind it. But N.W. was all along several hours 

 behind the others in its development. These might be 

 arranged in the order of development thus : — S., S.E., 

 N., C. ; but with smaller differences between them. 

 On the evening of the 6th August the umbilical stalk 

 and spiral had dwindled to a small dense inverted 

 cone with a rounded base and having its apex at the 

 annulus (v. Fig. 33). On its north side a sort of 

 notch separated the sharp curved bird-like beak from 

 the rest of the stalk. The clear central area was 



* In the'group of nine eggs I deduce this from Mr. Jeffrey's 

 observations communicated by letter. 



