SPERMATOGENESIS OF THE MYRIOPOlv-. 145 



er tlu- plain '- of longitudinal and cross division are establi>hed. 

 the further change- involve merely a shortening and condensation 

 of tin- < MI in- -tructure. In Fig. Ill, c, d, two stages in this pro< 

 an- -hown, lioth cleavages being very evident. L.ner, as the 

 omden-ai i<m i.mtinues these planes of cleavage are obscured to 

 -nine extent .md usually the only evidence we have of the longi- 

 tudinal cleavage i- a very definite notch at each end of the chro- 

 mosome, \\hile the plane of cross division is usually shown merely 

 b\ .1 >liyhtl\ [i d diameter of the tetrad near its middle (Fig. 



Ill,'/, - I me cases, however (Fig. 3, g, //), the plain- \ 



longitudinal and transverse cleavage may be seen very distinctly 

 ;i in the metaphase (Fig. 4. N, 13, ;/, 16, ;;, etc.). In nu ta- 

 kine-i- a longitudinal division is accomplished by a gliding apart 

 .| the i\\o h.il\i - of the tetrad (Fig. Ill, g, i) in a manner 



'iitialK -imilar to the division of the cruciform tetrads. 



In a number <>i the cells studied there seems to be one of the 

 rim mi"- HIM - <>l this type, which presents quite a different ap- 

 pearance dining the act of division. A constriction appear- in 

 thi- rhiomo-t.nic at about the middle point (the plane of tran 

 verse clea This is so pronounced that there is in many 



dependent on the stage of division) a partial or even a 

 (i.inpleie interruption of the chromatic material at this point 

 I igs. ;. \, |. N, 9, N, 10, N, etc.). From a careful study of thi> 

 dm uin i-iinir in inaiiN 1 cells, the conclusion seems inevitable that 

 thi- i me tetrad undergoes a transverse division, while the rest of 

 tin i hn mn '-miles are dividing longitudinally. 



A \aiiat i-'ii i>l the rod-shaped tetrad is shown in text-fig. IV. 

 1 hit alter the longitudinal cleavage has been established, the t\\ o 

 ilmad-, in-tead \ King side by side, are twisted about each 

 other in -iuh a \\a\ as to form a rope-like structure. The result - 

 IIH tapha-e chromosome differs somewhat in appearance fnmi 

 other- i.|' t hi- t\pe, although in all essentials it is identical. As 

 the thread- -Imrten the twisting gradually becomes less and less 

 pi.mniinced I i-. IV, b, c,d, e) until in the completed chromosomes 

 there i- onh a -li^ht twisting and usually the two part- merely 

 overlie ich other at an angle. The division accomplished by 

 the ln-t mat nr.it ion mitosis is a longitudinal one. 



He-itle- the-e three types of ordinary chromosomes all of which 



