STUDIES OF REPRODUCTIVE ELEMENTS: I. 



seen a ceJl whose chronititic elements are somewhat sliorter tliaii 

 those represented in tig. 6, and one at the right shows distinctly eight 

 short chromatic rods. 



The sperm motlier-cells increase all the while in size u]) to tin; 

 stage which we have called the zone of ripening ("lieifezone"), and 

 which we will now proceed to descrihe. 



c. The Zone of Eipening. — The eight chromatic rods now begin to 

 be c()]i:>trictcd at their middle point giving rise to eight dumb-bell- 

 shaped Ijodics as Ijefbre. Tliese arrange themsehes in the shape 

 of a ring a]id each ol them Ijecomes divided into halves on tlie appear- 

 ance of achromatic fibres as before (tig.-. 1), 10, and 11). In tig. i) 

 which is drawn from a specimen killed with liot picro-acetic solution, 

 the ei'dit chromatic elements are beiiinnini'' to di^'ide transversely, 

 while in the cells represented by tigs. 10 and 11 (treated with acetic 

 acid solution of methylgreen) the division has proceeded a little farther. 

 The large size of the cells represented l)y these tigures is due perhaps 

 to the pressure exerted upon them 1)y the cover-glass. The cells 

 resulting from this disi.-ion contain therefore each eight single chrijmcj- 

 somes, which noNv [)rcpare to divide dircdhj witJtuiU an inter vcniiuj 

 resting stage. The eight siugle chr(jmosomes in each of llie cells 

 after the division, arrange themselves in (jne plane, and mostly at the 

 periphery of a ring as usual, but somet:imes one or two chromosomes 

 can be foimd in the interior of the ring. These cells now begin to 

 be divided into two on the appearance of the attractive sphere, central 

 bodies, etc., as usual in the karyokinetic cell division, but with this 

 important difference concerning the chromosomes, that eaeh eiiiomosonte 

 does not heeoine divided into tn-o as usual, hut remains undivided during 

 the division, so that four of (he eight go hodiig into one cell and tlie 

 other four into the other. 



Figs. 12, 13, 14, 15, :!iid 1() represent i hese changes. In lig. 1:^, 



