472 M. Louise Nichols. 



As the network contracts about the prominent nucleolus the ends 

 of the chromosomes may be seen projecting from its border in pairs. 

 (Figs. I, 5-6.) Later they shorten and approach each other more 

 closely. 



In Talorehestia, on the other hand, I was not able to make out 

 with distinctness any parallel pairing of chromosomes. The first 

 premonition of synapsis is the appearance of long, slightly thickened 

 strands in the nucleoplasm converging towards the nucleolus. They 

 gradually grow denser, but for some time retain their connection 

 with the nuclear wall, while the rest of the nucleus condenses about 

 the nucleolus. (PI. 1. T, 5-7.) Finally, however, the entire net- 

 work is converted into V-shaped chromosomes with the exception 

 of a few delicate fibrils still stretching across to the nuclear mem- 

 brane. (Fig. T, 8.) 



The nucleolus of Talorchestia and Idotea is apparently more of a 

 factor in the synaptic changes than that of Homarus or Hippa. The 

 nucleolus of Talorchestia possesses considerable plasticity. Its shape 

 is not usually truly spherical ; it may be ovoid, more or less elongated 

 or sometimes drawn out into processes not unlike the pseudopodia 

 of an amoeba. It seems to form a center around which the nuclear 

 network contracts. In destained preparations its substance may show 

 the color in three degrees of intensity, indicating that it is not by 

 any means homogeneous. The nucleus of Hippa and Homarus per- 

 sists throughout the synaptic changes, but is to all appearances inde- 

 pendent of the chromatin. (PL 1. Hi, 11 ; Ho, 6.) 



Maturation Divisions. — The nuclear network of the resting sperma- 

 tocyte is in all delicate and stains only faintly. The condition of 

 the nucleolus varies in the different forms. In Oniscus it is not very 

 conspicuous, in Idotea much more so and always flattened against 

 the nuclear membrane. In Hippa it is very smaU and there are 

 frequently two. In Homarus it is rather prominent and occupies 

 approximately the center of the c^ll. (PI. 1. Hi, 14; Ho, 7; PI. 

 2. I, 11.) In all it diminishes in prominence during the prophases 

 and finally disappears. 



A stronger tendency to polarity in the formation of the sperma- 

 tocytic chromosomes is evident in Hippa than in the others, although 



