1 84 J- THOMAS PATTERSON. 



This part of the study has furnished many difficulties, because 

 of the fact that the capsule at this particular stage is very plastic 

 and hard to fix properly. Only a few cases of good fixation have 

 been secured: and in one of the clearest of these the nuclei are 

 seen to be surrounded by a finely granular protoplasm, about 

 which a membrane must later be secreted. 



2. The Aborting Spindle. The study of maturation and fer- 

 tili/ation was made- difficult by the presence of a spindle which 

 appeared in the egg some time before the egg capsule was set 

 free into the parenchyma. On account of its large size the spindle 

 was at first taken to be that of the first cleavage, but inasmuch 

 as the first division of the fertilized egg results in cutting off a 

 small micromere, it soon became evident that this interpretation 

 was incorrect. Furthermore, in the eggs in which the large 

 spindle appeared the most diligent search failed to reveal any 

 polar bodies. \Yhen this fact once became fully established 

 it was evident that we had in Graffilla a display of that remarkable 

 phenomenon of a "disappearing" or "aborting" spindle, first 

 discovered by Selenka, '81, and to our knowledge of which 

 Wheeler, Gardiner, and others have contributed. 



Selenka's discovery was made in connection with his work on 

 the polyclad Thysanozoon Diesingli. He describes the aborting 

 spindle as appearing in the uterine eggs. After the egg has 

 reached its full growth, the germinal vesicle begins to make prepa- 

 rations to divide in the typical manner; the chromatin forms a 

 spireme, the achromatic spindle with its two centrosomes appears, 

 and the chromosomes pass into the equatorial-plate position. 

 At this point the process stops, and the nucleus returns to a 

 resting condition. Subsequently the egg throws off two polar 

 bodies, is fertilized, and develops in the normal manner. Inas- 

 much as the yolk granules are evenly distributed throughout the 

 egg at the beginning of this peculiar phenomenon and are col- 

 lected about the astral centers at its close, Selenka supposes that 

 the function of the aborting spindle is to mass the granules at 

 the center of the egg. But this interpretation fails to explain 

 the appearance of the spindle in those eggs in which a collecting 

 of the granules about the astral centers does not take place, as 

 both Lang and Wheeler have observed. 



