288 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATORY. 



tocj^e mitosis, just before the separation of the dyads. The 

 cross form is merely a transition stage that the rod passes 

 through in its change from one axis to the other. Montgomery 

 says that "very rarely have the chromosomes an X-shape." 

 By "X" he probably means the cross shape. He is mistaken in 

 this, for the X or cross is a form that may always be seen in 

 any cell during the late prophase and the metaphase. He has 

 but one drawing (his fig. 31) showing a cross form, and for 

 that he gives no explanation whatever. From the way he has 

 drawn it one would judge that the univalent chromosomes 

 which constitute it were in conjunction at the middle of their 

 length instead of at the ends. But this view of the cross can- 

 not be brought into agreement with the form that the earlier 

 more open crosses of the prophase show (figs. 26, 29), where 

 the four parts to the tetrad, the chromatids, may with little 

 difficulty be traced from arm to arm, where it may be seen 

 that in this cross every chromatid forms a part of two arms 

 and no two of the chromatids continue together throughout 

 their whole length (cf. fig. 29). 



Before going further we must clear up the confusion about 

 the manner of the attachment of the spindle fibers to the chro- 

 mosomes. Montgomery's position upon this matter is not 

 clearly defined, but some idea of it may be gotten from the 

 following statement : "All the chromosomes become so placed 

 in the spindle that mantle fibers from one spindle pole are at- 

 tached to one univalent element, and mantle fibers from the 

 other spindle pole to the other univalent component of each 

 bivalent chromosome." If Montgomery had examined his 

 metaphase chromosomes more extensively and more carefully 

 he would have found many lateral oblique views such as 8 

 and 11 of figure 32, or in plates XXI and XXII, such as chro- 

 mosomes 11, 6 and 4 of series 2, or 11 of series 6, 10 of series 

 10, 7 of series 13, 12 of series 18, 6 and 4 of series 24, or 9 of 

 series 25, all proving beyond a doubt, when carefully studied 

 under the microscope, that the mantle fibers do not attach to 

 univalent halves of bivalent chromosomes. Instead, each fiber 

 is attached to the halves of the two univalent elements that 

 make up the bivalent chromosome, i. e., each fiber (and there 

 are but two fibers running to each ordinary chromosome, one 

 from each pole) carries off or leads off with it to its pole a 

 half of one univalent element together with a half of the other 

 univalent element that constitute the bivalent chromosome. Or 



