Spermatogenesis in spiders. 519 



During- this period the hétérochromosome elements retain their 

 affinity for the stain and persist as rounded nucleoli.^) 



Rest Period. In Maevia vittata, as in spiders generally, the 

 rest period is a very well defined stage and seems to persist for 

 some time. The autosomes have lost their affinity for the stain 

 almost completely, while the hétérochromosome elements appear as 

 very densely-staining nucleoli scattered through the nuclear cavity 

 (Figs. 12 to 23), Our interest in the period lies in the number and 

 in the behavior of the nucleoli. 



I wish to point out here that the Ehelich-Biondi-Heidenhain 

 triple stain has been used in order to determine if the nucleoli 

 found at this time were true chromatic structures, or whether they 

 were only plasmosomes. This differential stain showed quite clearly 

 that these bodies were true chromatin, and, furthermore, no evidence 

 was found for the presence of a plasmosome. Indeed, a plasmosome 

 has never been described in the spermatogenesis of any spider and 

 no trace of one has been found in this study of thirteen families. 



On a basis of the hétérochromosome constitution, we may divide 

 the spermatocyte cells of the rest period into two groups; a) cells 

 which contain two equal sized nucleoli, b) cells which contain more than 

 two nucleoli. The ultimate behavior of the two classes of cells is 

 the same, so that w^e may discuss this phase of the period together. 

 The variation in the number of nucleoli is of interest because it 

 shows the presence or absence of the peculiar chromosomes which 

 we have called ctetosomes. 



If we compare the cells shown above in Figs. 12 to 23, we 

 find that two processes are going on during the rest period. Most 

 striking, perhaps, is the fusion which takes place between the 

 nucleoli of the cells, such as is shown in Fig. 13 or 19. In 

 very young spermatocytes (Figs. 13, 14, 15) we find four 

 small nucleoli present in the cells, while in the cells shown in 

 Figs. 17 or 18, we have only two nucleoli; but they appear larger 

 than the individual nucleoli of the earlier stages. And in the cells 

 shown in Figs. 21 to 23 we find a fusion of the nucleoli into 

 one mass. 



Going hand in hand with this fusion of the nucleoli we find 



1) In the present paper the terra "hétérochromosome" has been 

 applied to all of the chromosomes which are not autosomes. It would 

 thus include both the accessory chromosomes and the supernumeraries. 



