242 BULLETIN OF THE 



is followed by important changes in the yolk. The cresceAt-shaped 

 space disappears. The " clear spot " passes from the conical to an oval 

 form, then becomes figure-eight-shaped, and finally appears as two dis- 

 tinct nuclei, which are distinguishable from the earlier condition by 

 reason of the sharp contour of the walls, and the presence of a large 

 nucleolus in addition to less prominent vesicles. These nuclei have an 

 eccentric position ; they lie nearer the point whence the polar globules 

 were detached. 



There can be no question about these nuclei being really the male 

 and female pronuclei. I have not, however, been able to discover in 

 either of them in the case of Limax campestris a single nucleolus of 

 greater size and refractive power than the other contained bodies. The 

 contour of these nuclei (pronuclei), says Warneck, grows indistinct, their 

 envelopes are dissolved, and the contents of the two form a single mass, 

 which, before the division of the yolk, becomes oval, and then biscuit- 

 shaped, with the long axis at right angles to the position previously (in 

 the conical clear spot) occupied (nucleus of first cleavage sphere *?). 



What Warneck has said of the cleavage of the yolk, as observed in 

 the living egg, is of less immediate interest, and from its substantial 

 agreement with the description given in the first part of this paper may 

 be passed with a few words upon a single point. Warneck says (p. 128) 

 that the plane of the first cleavage furrow is not perpendicular to the 

 long axis of the yolk, but cuts it at an angle of almost 45°. I have some- 

 times seen such an obliquity in the course of the furrow, though never 

 so great an angle, nor do I think it can be true for anything like a 

 majority of cases with Limax campestris. 



I return to his account of the clear nuclear spot. With the length- 

 ening of the yolk, and its constriction, the spot diminishes to one fourth 

 its former dimensions, and is only visible with difficulty, especially in 

 the case of Lymnseus.^ 



There can be no doubt, he very rightly affirms, about the dissolution 

 of the nuclear membrane and the nucleoli. This, and the failure of the 

 nuclear substance to curdle when exposed to water, lead him to the con- 

 viction that this clear spot has again altered its chemical properties, and 



* The somewhat incongruous statement that, for Lymnseus, this obscurity arises, 

 as he thinks, from the fact "that the contents of the nucleus mingle with the re- 

 maining yolk-mass, and that the spot (Fleck) withdraws -itself to the centre of the 

 yolk at the formation of the dorsal [i. e. at the animal polel furrow," could not have 

 outweighed in his own mind the direct observations of a division of the spot in the 

 case of Limax. 



