BLACKMAN. — SPERMATOGENESIS OF THE MYRIAPODS. 505 



Just as ill Lithobius sp. ?, the first nuclear change in the prophase of 

 the first spermatocyte concerns the chromatin in the karyosphere. 

 This leaves the dense masses and collects near the periphery either in 

 the form of coarse granular flakes or loose aggregations of small 

 globules. At the same time the achromatic deposits in the nucleus 

 break up into a number of diffuse, lightly staining masses (Figure 13), 

 which come into relation with the chromosomes as they arise fi'om the 

 karyosphere and become a part of them. 



The chromatin arises from the karyosphere (Figure 23) in the form of 

 small globules, which, as they leave the karyosphere, become embedded 

 in the diffuse masses of the achromatic substance. These masses of 

 achromatin lengthen out into short segments, and in each of these the 

 chromatin becomes arranged in the form of distinct darkly stained glob- 

 ules (Figure 23). Thus each of these composite masses at this time con- 

 sists of a diffuse, lightly stained baud of achromatic material, in which is 

 embedded a single row of intensely black globules of chromatin. These 

 globules at this stage are always of about the same size, and are always 

 spherical, presenting the appearance of droplets of liquid chromatin. It 

 is not always easy to observe the typical arrangement of the chromatin 

 globules, as the chromosome is often so bent, or in such a manner 

 distorted, as to obscure their linear arrangement. 



The changes immediately following the origin of the chromosomes 

 are similar in results to those in other animals. Each globule is divided 

 into two equal parts, so that the chromosome, instead of being com- 

 posed of a single row of chromatin particles, now consists of two such 

 rows (Figure 23), each of which contains the same number of globules. 

 This undoubtedly represents a longitudinal division of the chromosome, 

 as the linear arrangement of the globules doubtless has the same sig- 

 nificance as the similar arrangement of the granules in the ordinary 

 chromatin segment of the prophase. Following the longitudinal split- 

 ting, the transverse cleavage is accomplished in the same manner as in 

 Lithobius sp. 1 by a division of each row of globules at its middle. The 

 four chromatids thus produced may rotate upon each other in such a way 

 as to result in the typical cruciform tetrad (Figure 23), or may remain 

 a double row of granules with a gap between the two pairs nearest the 

 middle wider than that between any other two pairs. In Figure 23 

 two tetrads showing the typical cross-shaped form are shown ; these 

 are redrawn at the side of the figure with the achromatic portions 

 omitted and the globules comprising each chromatid connected by 

 lines, in order to show diagrammatically the author's interpretation of 

 their structure. 



Owing to the distortions of the arms of the tetrad, it is often difficult 



