6 C. ISHIKAWA. 



which is drawn from a specimen treated with acetic acid sokition of 

 methylgreen, and shows the eight single chromosomes in the e(|ua- 

 torial zone of a spindle, five of tliese are seen on one side while the 

 other three lie on the other side. The cell body appears to he larger 

 than those represented by figs 13. 14, and 15, which are taken fr(jm a 

 specimen treated with picro-acetic acid solution. This difference in 

 size is due partly to the pressure of the cover glass, but chiefly to 

 the action of the acetic acid. Fig. 13 shows the polar view of a 

 spindle at the stage of fig. 12. Of the eight chromosomes, seven lie 

 at the periphery and one in the middle of a circle. In fig. 14 a 

 .similar spindle seen irom the side is represented, while tig. 15 shows 

 the cell-divsion nearly completed, four chromatic elements being drawn 

 to one pole and foiu- to the (jther pole. The cell-body is also nearly 

 at the end-stage of its division. A similar stage is represented more 

 clearly by fig. 16. 



Tlie nucleus of a cell after this di\ision again acquires a 

 membrane and the cbromosomes become also indistinguishable, colour- 

 ing \ery deeph' and unilbrmly. At a place a little farther outward 

 the nucleus ao-ain becomes uneven to the staininii- and shows more 

 or less distinctly indications oï chromosomes coming t(j occu])y posi- 

 tions at the periphery of the luicleus Avhose central part now shows 

 a clear space. In this condition the sperm cells again begin to 

 grow gradually, and the chromosomes come again to be seen more or 

 less distinctly as \evy fine threads and lying rather irregularly in the 

 nucleus. In this growth of the cell, the nucleus progresses more than 

 the cell bod}^, so that the latter becomes proportionally much reduced, 

 and when the cell passes into the vas deferens no trace of the cell-body 

 can be detected. The nucleus now assumes the characteristic elongated 

 sha|)e we find in the s])erm cells contained in the spermatophore sac 

 attached near the female opening. Illustratifjns of these changes are 



