162 W. H. LONGLEY 



suggested that a mitotic di^ ision had really occurred. The first 

 polar body as found with normal eggs usually shows a regular, 

 more or less elliptical outline, but it may present a lobed or frag- 

 mented appearance, possibly artificial, or indicating the initia- 

 ation of regressive changes. 



The second polar spindle 



The chromatic portion of the second polar spindle is very 

 speedily organized from the residuum of chromatin after the expul- 

 sion of the first polar body. Like the germinal vesicle and first 

 spindle it may lie, in sections of preserved material, at either pole 

 of the egg or at any intermediate peripheral position. In the 

 preparations studied by the writer it has always appeared per- 

 pendicular to the surface of the egg (figs. 9-10). As a rule it 

 appears near the first polar body, i.e., the latter suffers little 

 displacement. 



The achromatic portion of the second polar spindle is often 

 very much reduced, and the combination of this feature with 

 the arrangement of the chromosomes in practically one plane is 

 characteristic of many spindles of this order. However, apart 

 from the presence of the first polar body the best criterion serving 

 to distinguish the spindles is the condition of the chromatin. In 

 this connection there are at least three points to be noted. First, 

 the difference in mass between two dyads is only half tliat which 

 exists between the tetrads from which they are derived. There- 

 fore the chromosomes of the second will vary less among them- 

 selves in size than those of the first spindle. Second, the first 

 spindle soon proceeds to division. Its tetrads become divided 

 and the chromosomes may be scattered throughout the greater 

 part of the length of the spindle, corresponding d.yads being seen 

 in the two halves. Since the dyads of the second spindle do not 

 divide until the sperm head enters the egg, this relation cannot 

 occur in a second polar spindle in an ovarian egg. Third, a dyad 

 usually shows some indication of being composed of two reniform 

 bodies with their concave faces approximated. A narrow light 

 area frequently appears between them. 



