2i6 BIOLOGICAL LECTURES. 



tinuously and a spindle develops between them, so that by the 

 end of the maturation-period the egg contains a huge amphi- 

 aster with extensive rays. The recession of the egg-nucleus 

 appears to be influenced by the presence of this amphiaster 

 and the sperm-nucleus. The development of the yolk-lobe 

 would seem almost certainly to be correlated with the develop- 

 ment of the cleavage-amphiaster, since the various phases in 

 its growth and resorption correspond with the definite phases 

 of the cleavage mitosis. Nevertheless, in the unfertilized eggs 

 stimulated with potassium chloride the two maturation-divisions, 

 the reconstitution of the egg-nucleus and its inward migration, 

 and even the protrusion and resorption of the yolk-lobe, take 

 place in the constant and orderly sequence which is character- 

 istic of the fertilized eggs, though there is nothing in them 

 corresponding to the sperm-nucleus or sperm-centres. In the 

 one case, when the yolk-lobe is formed, the Qg^ contains an 

 enormous amphiaster; in the other, no amphiaster or radiations 

 are present. 



Although the unfertilized egg will remain in the normal sea- 

 water for several hours without apparent change of form and 

 without loss of "the capacity for maturation and fertilization 

 yet, if it is stimulated with potassium chloride, not only do the 

 phenomena of maturation ensue, but, after about an hour and 

 a half, the ^gg begins to break up into more or less irregular 

 segments, which frequently resemble the ordinary cleavage-blas- 

 tomeres. The karyokinetic activity se^isu strictu does not stop 

 with the reconstitution of the egg-nucleus; but, though the 

 sperm-nucleus, amphiaster, and centrosomes are absent, the nine 

 constituent chromosomes divide and the daughter-chromosomes 

 swell up into vesicles which usually remain in one cluster or are 

 irregularly scattered about, and resemble those found in the 

 telophase of ordinary mitosis. At this stage, however, the egg 

 is no longer devoid of radiations. On the contrary, an enor- 

 mous system of fibers radiates from the centrosphere, which 

 surrounds the group of vesicles and extends in all directions to 

 the periphery. The rays have the appearance characteristic of 

 normal mitosis when the chromatic vesicles have reached this 

 particular stage of development. Not infrequently, when by 



