ORIGINS OF AGAMIC PATTERNS 627 



external to the spermatid and certainly shows a definite relation to the 

 accessory cell, as does the axial fiber. 



Studies of spermatogenesis have usually been concerned with the sperm 

 cell alone and have given little attention to the question of possible de- 

 termination of its polar pattern by factors external to it. However, in 

 many accounts of spermatogenesis extensive changes in position of cen- 

 triole, acroblast, etc., are described." Axiate pattern of the spermatozoon 

 in many forms develops after the final division by changes in relative 

 position (sometimes of almost 180°) of distinguishable parts of the cell. 

 If the pattern is inherent in the cell, these shifts in position seem difficult 

 to account for, and they have usually been merely described without any 

 attempt at interpretation. But if they represent reaction of different cell 

 constituents to a differential or other factor external to the cell, the diffi- 

 culty of interpretation is certainly lessened. 



Cytophores or other accessory cells are entirely absent from spermato- 

 genesis of some forms; nevertheless, a spermatozoan pattern develops. 

 Cytological studies suggest that pattern may be determined by the final 

 cell division, as it apparently is in certain plant spermatozoids, the centro- 

 some-nucleus axis determined by direction of division becoming the sper- 

 matozoan axis, with the tail, when present, developing from the centro- 

 somal pole. This axis probably becomes the sperm axis unless an axis in 

 different direction is determined by reaction to some external factor, such 

 as cytophore or accessory cell. 



UNICELLULAR ASYMMETRIES : QUESTIONS AND SUGGESTIONS 



Development of a polar axiate pattern in animal spermatozoa appar- 

 ently precedes appearance of spirals and specific asymmetries. This 

 seems also to be true for plant spermatozoids with spiral patterns, but 

 in those the primary pattern is usually merely that resulting from the 

 final cell division. In general, the spiral patterns and specific asymmetries 

 seem to develop secondarily in a definite orientation with respect to the 

 primary pattern. Moreover, they appear to be associated with a high de- 

 gree of morphological structurization and differentiation rather than to 

 represent a general property of protoplasms. As regards the protozoan 

 asymmetries, it may appear at first glance that there is no such distinc- 

 tion between a primary axiate pattern and secondary asymmetries. In 

 protozoan fission the patterns of the daughter individuals are not entirely 



" For figures and description of cases see E. B. Wilson, 1925, pp. 356-85. Many others are 

 given in the literature of spermatogenesis. 



