SMALLWOOD : MATUKATION OF HAMINEA SOLITARIA. 285 



living egg, it was noticed that small cells containing deutoplasmic 

 granules, and much larger than the usual polar cells, were occasionally 

 formed at the time when the first polar cell ordinarily appears. These 

 small cells were watched until the egg passed into the two-cell stage, 

 which occurred at the usual time. There was so much albumen in the 

 egg capsule that it was very difficult to follow the fate of the small cells 

 with any certainty, so that I am unable to say positively that they 

 divide, as the presence of the spindle in Figure 37 would .lead us to ex- 

 pect ; but the facts that they were produced in the living egg at precisely 

 the time the first polar cell appeared in the surrounding eggs, and that 

 the same conditions were afterwards found in preserved material at 

 this stage, make it highly probable that we have here a very much 

 enlarged polar cell. These observations support the generally accepted 

 view, first advanced by Mark ('81), that the polar cells are abortive 



eggs. 



(|3) Longer or Indirect Process. 



The second process or method of the formation of the second matura- 

 tion spindle is more elaborate. The conditions in Haminea are usually 

 so evident that there can be no doubt as to their occurrence. In this 

 process the chromatic substance passes through a stage which resembles, 

 more or less closely, the condition of the so-called resting nucleus ; the 

 chromosomes become surrounded with a nuclear membrane, the cavity 

 of which is traversed by linin fibres, but the chromosomes do not 

 lose their individuality. 



One of the most noticeable facts in this process is the lack of syn- 

 chronism between the changes in the centrosome and those in the 

 chromosomes. A sequence based on the changes in the chromosomes 

 would, for example, place such a stage as that represented in Figure 42 

 (Plate 7) before the one shown in Figure 39. After the chromatin 

 passes into the nuclear-vesicle condition, it remains for a certain period 

 without change of form or position while the achromatic figure is under- 

 going a number of important alterations. Wilson (-.01'') has shown, by 

 results obtained experimentally, that the centrosome may act inde- 

 pendently of the chromosomes. The case of Haminea is the more 

 interesting because in it the process is normal. 



In describing this process, the progressive changes in the achromatic 

 figure of the second polar spindle have been taken as the basis for deter- 

 mining the sequence of events.^ If the conditions of the chromatin 



1 In selecting tlie progressive elianges in the achromatic figure as the basis for 

 determining the sequence of events, my purpose has been to emphasize the history 

 of the changes in the second polar spindle. 



