KARYOKINESIS. 



11 



arms which lie in the spindle axes lengthen, while the transverse arms shorten, the 

 hole disappearing ; in this way chromosomes are formed with three enlargements (C, 

 4 and 5) similar in all respects to those described above (B, 4 and 5). The resemblance 

 of these two forms is so close that it is difficult to explain the differences in their 

 mode of origin. It is possible that forms, such as those shown in B, 4 and 5, are 

 really crosses with short transverse arms, the tips of all four arms being bent toward 

 each other until they nearly or quite meet. 



The striking differences in the shapes of the chromosomes of the prophase is 

 continued into the metaphase where at least three distinct types may be recognized 

 as shown in text fig. I, lines A, B and C. In the late anaphase, however, all come 

 back to a cubical or tetrafoil condition ; a hole is usually present through the 

 middle of these as in the prophase. 



2 3 4 



«O0) t 



>093 { 



Prophase 



6 7 8 9 



t i 



H3 



] 



•n t 



Metaphase 



t » 



t 



T o 



* o 



* • 



of the First Maturation Division of Crepidula. 



Various authors have called attention to the variety in the form of the chro- 

 mosomes of the first maturation division (v. Klinckowstrom '96, Van der Stricht, 

 '98, Foot '98, Lillie '98, Griffin '99). Foot and Lillie figure 3-part chromosomes in 

 the metaphase of the first maturation of Allolobophora and Unto entirely similar 

 to those in Crepidula, and Lillie shows these chromosomes split longitudinally, as 

 they must be, if formed from crosses as shown in text fig. I, line C. 



It is difficult to say whether these differences in the shapes of chromosomes 

 mean much or not, On the one hand it is possible that all the chromosomes of a 



