no ^ George Lefevre 



however, are soon interrupted, for the latter usually break away 

 from their original position, and either pass into the cleavage 

 space or float freely about in the perivitelline fluid. Torrey ex- 

 plains the presence of the threads by supposing that, when the 

 membrane separates from the egg, the protoplasm adheres to 

 the corrugations on the inner side of the membrane, and, because 

 of its viscid nature, is drawn out into the threads. If the mem- 

 brane is merely the denser surface layer of the egg which is 

 mechanically lifted up as a result of the expression of a liquid 

 secreted by the egg, as Loeb ('05e, p. 155) is inclined to believe, 

 the formation of the threads can be readily explained. Fig. i, which 

 is drawn from the living egg, shows these strands of denser super- 

 ficial cytoplasm in an egg which has already maturated and formed 

 the first cleavage amphiaster. 



2 Formation of Polar Bodies 



The first visible change in the interior of the living egg, after 

 transference from the acid solution to normal sea-water is the 

 bodily migration of the germinal vesicle from a position near the 

 center to the animal pole of the egg. This change in location, 

 which may be seen by comparing Figs. 2 and 3, drawn from sec- 

 tions, does not always take place, but it has been observed in a great 

 many cases. In the normal egg the migration does not occur, 

 but the germinal vesicle breaks down near the center of the egg 

 and the first polar spindle later rotates into a radial position, with 

 the outer aster close to the surface, in the usual manner. In the 

 parthenogenetic eggs, however, owing to the outward movement 

 of the germinal vesicle, the spindle arises, as a rule, considerably 

 nearer the surface of the egg. 



The extrusion of the first polar body takes place in from 45 to 

 90 minutes after removal from the acidulated water, thus showing 

 a great retardation of the maturation, since in the normal egg the 

 first polar body is formed in about 20 minutes after the entrance 

 of the spermatozoon. It soon moves away from the surface of 

 the egg and the second arises immediately under it and very 

 shortly afterward, although the interval between the appearance 

 of the two is more variable than in normal maturation. 



