Spermatogenesis in spiders. 531 



second type of chromosome, we have the two parts separated as 

 shown in Figs. I and J. 



After the first division the autosomes enter into a socalled 

 resting period when they become diifuse and lose their affinity for 

 stains. This stage persists for a short time and then the autosomes 

 of the second division are formed. As they are drawn into the 

 spindle they are very long rods more or less bent (Figs. L or M). 

 It does not seem wise to take up a discussion of the question of 

 reduction until after we have followed the course of the chromo- 

 somes in the other forms of spiders. 



Spermatogenesis of Tufted variety of llaevia vittata. 



The observations set forth in the following description are based 

 on sections from five fully mature males. In fixing the abdomens 

 and in staining sections the same fluids were employed as in the 

 case of the gray variety. My material is fully mature so that it 

 has not been possible to follow the changes in the sperm atogonial 

 cells. In all of the general processes going on in the germ cells, 

 the tufted variety of males does not difter from the gray variety 

 so that we may pass over many of these points in the following 

 description. 



The rest stage does not prove instructive in my material, the 

 testis being too mature to aff"ord anything but cells in which fusion 

 had taken place between the nucleoli. 



Leptotene stage. The most interesting feature of this 

 stage is the behavior of the hétérochromosome elements. We find 

 the accessory chrososome appearing as it did in the gray variety; 

 either as two rods lying side by side, or else as one general mass, 

 and in addition to this, we often see another small but densely staining 

 body lying free among the threads. As we shall see, this represents 

 a "planosome'Vj that is, a supernumerary chromosome which wanders 

 through the two maturation divisions. 



It is impossible to say what proportion of the cells show this 

 planosome for the leptotene-threads hide it from view except when 



1) The term Planosome (TtXav^g a wanderer) was adopted for the 

 peculiar supernumerary chromosome of spiders which has no regular 

 mode of distribution and whose ultimate fate is a matter of chance. 



