! 7 - EDITH PINNEV. 



naled chromo-onu - in tin.- hyhrid-. Kilt/er make- IK > com pa rise m 

 hetwcen tin- equatorial plates of the species thai In- studied. 

 In hi- figures of aiiaphases of different species the daughter 

 chromo-omes an- -hown as rods of equal thickness. IK- regards 

 the apparent variation- in tin- thickness of the rods in seciion- 

 staincd with Heidenhain's iron-haematoxylin as tin- fault of the 

 stain and hi- c< >ncli!-ion- as to tin- uniform thickness of the n>d- 

 are drawn from observations made upon aceto-carmine prepara- 

 tion-. ( )nc would naturally expect to find the rods which lie 

 farthest from the surface of the section retaining the stain longest. 

 The deeper lying rods might then appear thicker hut all of the 

 rods K'ini; in one optical plane \\otild >how the same width. 

 All of the rod- in one optical plane, howe\er, an- not of the same 

 width. It might In- argued that a di-turhance in the section 

 alter staining or variations in the thickness of the- sections would 

 produce thi- effecl hut tin- variations in width an- of too frequent 

 occurrence to he a-rrihed to any such causal factor-. 



I am convinced from my own ohservation- that the rods of 

 one -pindle not only vary in thickness as they are drawn toward 

 the polo hut they vary irregularly. The explanation is simple. 

 I hiring division the proximal ends of the two halve- of a rod 

 are drawn toward opposite poles while' the distal ends are still 

 united. This latter opposing force results in the lengthening 

 ot the two daughter chromosome- during their separation. As 

 soon a- the separation is complete the rods hegin to contract. 

 Since some rod- are much longer than others the accomplishment 

 oi their separation and their subsequent contraction would 

 naturally he delaved and their relative lengths in a late anapha-e 

 would he more apparent than real. 



For illu-tration I ivler to Ralt/er'- later paper, 'lO, Fig-. T, a 

 and /;. In these he sho\\ - a Strongylocentrotus spindle with only 

 two rod-shaped chromosomes over eisjit mm. long. The l\\o 

 -pindle- sho\\n in hi- Fi^-. 4, <i and . and u, n and h from the 

 same -pecie- each show three rods which exceed eight mm. 

 On the other hand Fii;-. 5, n and /. sho\\- thirteen and Figs. 6, 

 a and b, ten chromo-ome- from one spindle \\ Inch are mon- than 

 ei-ht mm. loi 



Again P'igs. 5, a and ! >, -ho\\ om- chromosome over 15 mm. 



