BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDRA. 45 



5. Maturation Divisions in the Small Spermatocytes. 



I have shown that the cells of the type of small spermatocytes are 

 distinguished in the vesicle stage from those of the large type hy the 

 following characteristics : they are much smaller, the diameter being 

 but about one half that of the larger type ; they are not connected in 

 pairs by a persisting spindle, each cell being entirely distinct ; they are 

 not arranged in any regular manner in the follicle, since they are so 

 crowded that any regular arrangement is impossible ; they are so forced 

 together (Plate 5, Fig. 56) that their outlines become polygonal (i. e. they 

 are more like ordinary testicular cells). They also differ from the large 

 type in the relative sizes of the different parts, being characterized by a 

 smaller amount of cytoplasm and archoplasm and a relatively greater 

 amount of nuclear material. These discrepancies, if unaccompanied by 

 differences in the later behavior of the cells, would not be sufficient to 

 warrant their treatment under a separate heading. However, as the 

 subsequent differences are even greater than those in the vesicle stage, 

 I believe such a division is necessary for the more perfect understanding 

 of the spermatocyte changes. 



These cells offer an excellent example of the effect which an appar- 

 ently small difference in the surrounding conditions may exert upon 

 slightly differentiated cells identical in origin and early behavior. The 

 conditions up to the time of the formation of the karyosphere are appar- 

 ently identical (Fig. 1). After this, however, the conditions around part 

 of the cells show a considerable change, which seems to exert an immediate 

 and powerful influence upon the further development of these elements. 

 Later (viz. in the second spermatocyte) the conditions around the cells of 

 the two types again become similar, and their behavior is then practically 

 the same, notwithstanding the difference in size of the cells and the small 

 difference in structure. 



The germ cells of this animal are very slightly differentiated from the 

 typical cell, and seem to be in a very plastic condition, since they are 

 apparently easily acted upon by external conditions. This is shown not 

 only by the separation of the spermatocytes into two types, but also by 

 the behavior of the abnormal cells described on a preceding page. This 

 plasticity of the cells is at all times very striking ; indeed the extent to 

 which the behavior of the cell is modified by seemingly slight influences 

 is often nearly incredible. 



"We have seen that in the spermatocyte of the first type the hist 

 change noticeable in the prophase concerns the centrosomes and archo- 



