HETEROCHROMO-MML;-, ix THE GUINEA-PIG. 161 



form of crosses. The rods are probably lateral views of cross- 

 shaped forms. Fig. 17 shows 2S chronio-, mie- in an equatorial 

 plate. Fig. i > i- another metaphase in which tin- members of 

 the heterochromosome pair are ah-' -eparating earlier than 



the others. In Fig. 19 tin- separation ot some of the chromo- 

 some- as rod- ami V- in metakiiic-i- ma\ n. Fi^. Jo i- a 

 laii- anapha-e in which the heterochromosome pair is still un- 

 divided. This is unu-ual. but >ln>ws a kind of variation which is 

 iceable through all of the spermatogenesis. Varia- 

 tion is nio-t eon-picuon- in the pn>pha-e- of the fir-t maturation 

 mito-i-. As a rule one find- such earl\ prophasi are sho\\n 

 in I -"i;;-. i.} and 14, and the ehromoM .mes of the \oim- spindle 



\\i-ll on their \\a\ in the process of mctakiii' 

 bin one -oineiiiiie- hn!- the ehronio-oine- of an older sj)indle 

 much K-- I.M- aloii-^ touai'd di\i-ion than in I ig. 21, 

 and not infrequently I ha\< . ond,-n-ed ^pirenie. as in 



I . ell, the nuclear membrane having disappeared, 



and a -pindle formil ' - nnisi, I think, be an 



\\hiih maturation t. 



place at dilieiein linn--, and prob.ibl\- under different stimuli, or 

 stimuli ot diffen in ini- ' 24 is an inn anap! 



-ho\\in. the lar.c chroino-r une pai' as a pair of \ '- 



illslead ot ,\o||Id lia\e beell e\|ieeli'd Ifom ! 



i In tin- pn parations from one animal I repeatedly saw the 



largest chromo-oim : io\\n in Figs. J.s. - 1 ' and 27, a -:.lit 



band forming ill a later Si Lge Fig. J7 . Ill all tiler 



mail-rial the la- mosome ha- appea in l-'i^. 15, 



\\hich. lo-i-ther \\ith l-i-j. ^4. SUJ lhat the four end- of the 



t\\o |,,n w chromo-ome- \\hich lorm the |.:ir an- usually |o|di-d 



I he t\\o lateral hakes of the cro-s sho\\ n in I ij. l~ 



f ild i d together would give the form shown in I ig. i .=,-/. and mi- In 



then -epaiMle as ii: ' '. The -ame kind of folding ha- very 



lil .-i !\ occurred in hromo-dine- 5 and l<) in the -lioun 



in Fig. [6, and po--ibl\ in ..tin - uhere it i- less -\ident. 



' i\D M'l-.KM \ I'" N II-. 



Hi-i\\een the t\\o maturation m 'hen- i- a res ge in 



\\hich the pa ; r- of second spermatocytes may often be found 



