4 W. K. BROOKS ON THE 



enlarges, and the shell itself is stretched and pushed out, away from the embryo, 

 as if this were hollowing out a place for itself in the surrounding gelatinous matter ; 

 but as both the outer and inner surfaces of the egg shell are well marked and clearly 

 visible, there can be no doubt that it is a real membrane, and the albumen of the 

 egg capsule must therefore either be absorbed through it or drawn in through the 

 micropyle. One axis of the egg is nearly twice as long as the other ; the micropyle 

 is situated at one of the ends, and the two ends are alike in outline. The yolk y, 

 is elongated in about the same proportion with the egg shell, and the long axis is 

 nearly parallel to that of the egg shell, but its surface is not concentric with the 

 inner surface of the latter, since one end of the yolk is much more rounded than 

 the other. The pointed end is the one upon which the blastoderm makes its appearance, 

 and is invariably turned towards the micropyle of the egg shell. 



The space h, between the egg shell and the surface of the yolk, is filled by a clear, 

 transparent, albuminous fluid, which does not, at first, present much difference from that 

 outside the egg shell, but as the embryo develops, the albumen inside the shell gradually 

 becomes liquid. A number of small, spherical, highly refractive particles were visible in 

 this fluid, and they were especially abundant around the micropyle, and on the surface 

 of the yolk. Owing to the spherical shape of the egg I was not able to use a mag- 

 nifying power of sufficient strength to detennine whether they were s^Dcrmatozoa or not. 



The yolk is transparent, highly refractive, and with a low power it appears perfectly 

 homogeneous, but with higher powers it is seen to be packed with oil drops of various 

 sizes, with very faintly marked edges, and a refractive index about the same as that of 

 the more fluid portions of the yolk. At the earliest stage which I found, the blastoderm 

 c, was well developed, and was perched, like a cap, upon the pointed end of the yolk, 

 which, as already stated, is the end which is nearest the micropyle. The cells of the 

 blastoderm are not very well marked in a living egg, but when treated with borate 

 of carmine fluid, to which a very small quantity of one-tenth per cent, solution of osmic 

 acid has been added, they become very conspicuous. Figure 4, plate 1, represents the 

 edge of the blastoderm of the egg shown in figure 1, after it has been thus treated. 

 The centre of the germinal area is occupied by a number of small spherules which are 

 irregularly spherical, and each of which contains a very large nucleus. 



As we pass from the centre of the cap towards the periphery, the spherules become 

 larger, and at its growing edge they are replaced by large flattened pyramids b, h, which 

 radiate out on all sides, upon the surface of the yolk a, and gradually jDass into the 

 surface of the yolk, without any distinct boundary at their outer ends. 



Careful examination shows that the segmentation spherules are pretty regidarly 

 arranged with reference to these j^yrtirnids. Just inside the broad inner ends of the 

 pyramids there is a ring of large spherules, c, equal in number to the pyramids, and 

 presenting every indication of having been just formed by the separation of the proximal 

 end of each pyramid from the larger distal portion. Inside these there is a second 

 ring of spherules, d', about half as large, and exactly twice as numerous as the first set, 

 and so placed that a pair of the spherules of the second set are pretty nearly in a 

 straight line with one of the first set and the base of a pyramid. Each pair of this set 

 is obviously the product of the division mto two of a spherule like those of the set c, 



