CHANGES IX THE EGO. 5 



interval of two to four liours may elapse before renewing the water. A.s 

 it is extremely difficult to change the water after the embryo.s have 

 hatched and are swimming freely about in the jar, without losing many 

 of them, it is advisable, before they hatch, which is about ten hours after 

 tlie fecundation, to reduce the water to a minimum volume, and then 

 simply to add a little fresh sea-water and remove the contents of the 

 vessel to larger and larger jars. In this way the water can be main- 

 tained sufficiently pure, until the young embryos have taken the habit 

 of swimming near the surface, when it may all be drawn off by means 

 of a siphon. A great deal of time and trouble will be saved 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 spo.wning, the eggs in the ovaries 

 are so closely packed that they are pressed into all sorts of shapes, tri- 

 angular, 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 3'olk is 0.75, the germinative vesicle 0.22, and the germinative dot 

 0.08. The formation of the Q^g 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 imbedded in the thickness of the 

 outer envelope, and are sometimes so crowded as to forni a halo round 

 the egg (PL 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 prevailing among 

 Physiologists, 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 still existing in our knowledge concerning the envelopes 

 of the yolk in the different branches of the animal kingdom. We do not 



