Chap. I. CHANGE S IN THE EGG. 5 



by this mode of procedure, and fewer specimens lost. The jars containing the eggs 

 should be kept in a cool place ; the most convenient method of securing a low and 

 even temperature is to place the small jars in large tubs filled with cold water. 



Changes in the Egg. — At the time of spawning, the eggs in the ovaries are so 

 closely packed that they are pressed into all sorts of shapes, triangular, polygonal, 

 elliptical ; but when placed in water, and allowed to remain a short time, they soon 

 become perfectly spherical (PI. I. Fig. 1). The following numbers are the ratios of 

 the diameters of the yolk, the germinative vesicle, and the germinative dot, the 

 outer envelope being 1 : the yolk is 0.75, the germinative vesicle 0.22, and the 

 germinative dot 0.08. The formation of the egg in the ovary, and its changes up 

 to the time of spawning, I have had neither time nor opportunity, thus far, to 

 examine. 



The spermatic particles, which swim about with great rapidity on escaping from the 

 spermaries, soon find their way to the outer envelope of the egg to which they 

 attach themselves, beating about very violently the whole time. The particles remain 

 embedded in the thickness of the outer envelope, and are sometimes so crowded as to 

 form a halo round the egg (PI. I. Figs. 1-4). I have not, in a single case, seen 

 any of the particles penetrate through the outer envelope and reach the yolk itself 



Probably a great deal of the difference of opinion which prevails among Physiolo- 

 gists, as to whether the spermatic particles penetrate through the successive envelopes 

 of the egg to the yolk itself, is due to the want of precision there still exists in 

 our knowledge concerning the envelopes of the yolk in the different branches of the 

 animal kingdom. We do not know whether what we call the outer envelope of 

 the egg of an Echinoderm is homologous to the outer envelope of the egg of an 

 Acaleph, of a Polyp, or of Worms, Insects, or Crustacea, or how far these envelopes 

 are found in the ovarian eggs of Mammals, Birds, Keptiles, and Fishes. And 

 before we can come to a satisfactory result as to the place in the egg which 

 the spermatic particles reach before changes can be observed to take place in the 

 yolk, the eggs of the different classes of Animals must be carefully compared with 

 reference to this point. The first phenomenon which precedes any change in 

 the egg is a rotary motion given , to the whole egg by the constant beating of 

 the spermatic particles ; the germinative vesicle disappears (PL I. Fig. 2) soon after 

 this, and next the germinative dot (PI. I. Fig. 3). The yolk has then all the 

 appearance of an egg which has undergone segmentation, and the yolk of which 

 should consist of innumerable small spheres. The yolk has the same granular 

 structure previous to segmentation which has usually been considered to belong 

 to it only after the segmentation is complete. The resemblance between these 

 two stages is still more marked in the eggs of Ctenophorse, where the ratio 

 between the diameter of the yolk and that of the outer envelope is large, and 



