MUSEUM OF COMPARATIVE ZOOLOGY. 181 



short time tangent to the vitellus ; but soon there appears between 

 the two a perceptible interspace, which continues to increase for some 

 minutes. The polar globule occasionally becomes removed a distance 

 equal to its own diameter ; more frequently, it is somewhat nearer the 

 vitellus when this separation ceases. It often remains for some time at 

 a distance from the vitellus, and then the interval gradually diminishes 

 again. At first I was inclined to think this might be due to a slow change 

 in the form of the vitellus, and that the motion of the polar globule was 

 consequently more apparent than real ; but the more I have watched it, 

 the less have I been able to satisfy myself that such is really the case. 



About an hour after the appearance of the first polar globule, — dur- 

 ing which the external form of the yolk has remained without noticeable 

 change, the crescent-shaped accumulation of clear protoplasm has disap- 

 peared, and the clear spot has become obscured, and again more distinct, 

 — there begins again the accumulation of clear protoplasm at the ani- 

 mal pole, which, as before, varies much in its extent in difterent eggs. 

 (Figs. 5, 10:) 



Two or three times I have noticed just at this epoch a very peculiar 

 behavior on the part of the first polar globule (Figs.11-13). It seemed 

 suddenly to give way on the side directed toward the vitellus ; and its 

 substance, which became as suddenly changed from almost complete 

 transparency to a granular and opaque condition, was rapidly projected 

 toward the animal pole of the yolk, with which it seemed to come in 

 contact. This certainly does not always occur, nor can I offer any sat- 

 isfactory explanation of its occasionally happening at this particular 

 instant, i. e. just before the first appearance of the second polar globule. 

 I have thought it might be due to the possibility that a change in the 

 form of the yolk causes the rupture of an unobserved delicate connecting 

 filament of protoplasm. But that does not seem very probable, inasmuch 

 as the distance between the vitellus and the globule is such as to allow 

 the discovery of such a thread of connection, if one really exist. 



Occasionally there is to be seen in the yolk at this time a second clear 

 spot, which lies much nearer its centre than the one which has now 

 come to the surface and has become partially lost in the crescent of 

 clear protoplasm. Usually one sees nothing of this deeper spot, owing 

 to the abundance and opacity of the vitelline granules. 



The changes which accompany the production of the second polar 

 globule are so nearly identical with those which mark the appearance of 

 the first, that attention need be called to only a few points in which 

 they seem to diifer. 



