334 PROCEEDINGS OF THE AMERICAN ACADEMY. 



With the reappearance of the nuclear membrane the cell enters upon 

 a period of phenomenal growth and the nucleolus increases in size very 

 rapidly, while the accessory chromosome remains of nearly the same size. 

 Stages in this growth of the nucleolus are shown in Figures G, 7, and 8, 

 b, c, d, e. As the nucleolus grows it also changes in its reaction to stains, 

 and assumes the diffuse brownish tint characteristic of the plamosome 

 when stained with iron-hamotoxylin (Figure 8 c). Its shape also is so 

 altered that from now on it is au approximate sphere, upon one side of 

 which lies the deeply stained accessory chomosome. This body, which 

 has a^ain assumed an oval shape, is usually not embedded in the plasmo- 

 some, but is closely apposed to one side of it (Figures 8 f, 9). Quite often 

 there is a cupdike depression in the plasmosome at the place where the 

 accessory chromosome comes iuto contact with it (Figure 10). 



It is during the period represented by Figures 4 to 19 that the most 

 striking and interesting differences between the germ cells of Scolopendra 

 subspinipes and S. heros occur. These variations, as I have already in- 

 timated, primarily concern the arrangement and behavior of the chro- 

 matic structures. 



The conditions in S. heros are briefly as follows : Upon the recon- 

 struction of the nuclear membrane after the last spermatogonia! division, 

 the cells, now containing the number of chromatin segments charac- 

 teristic of spermatocytes, " enter upon a period remarkable for the 

 extraordinary changes which take place in their structure." Of these 

 changes the most remarkable are the enormous increase in the size of the 

 cells and the peculiar and characteristic arrangement of the chromatin. 



Concerning the growth of the cells iu S. heros it is sufficient to 

 say that the diameter of the large spermatocytes is about ten times 

 that of the spermatogonia from which they arise. As regards the 

 chromatin structures, I may quote from one of my papers cited (:03) : 

 " As the cell continues in its growth the chromatin segements become 

 larger and more diffuse. They no longer retain the stain with the per- 

 sistency which has characterized them heretofore. Gradually they break 

 down and their substance is accumulated about the accessory chromosome, 

 thus seemiugly increasing this element greatly. This process continues 

 until all of the chromatin of the cell is aggregated in one large, intensely 

 staining body situated peripherally in close contact with the nuclear mem- 

 brane." This body, the karyosphere, is not a homogeneous mass of 

 chromatin, but, "on the contrary, is a rather complex structure, con- 

 sisting of chromatin, liuin, and karyolymph." The chromatin composing 

 the karyosphere is in the condition of a very fine spireme, which is so 



