B. F. Kingsbury 1^'^ 



the second division of the cell follows the first without any resting 



period. 



A second point of view from which the chromosome forms may be 

 considered is that of their manifest tendency to fuse. Thus, ring- 

 formation typically occurs by the fusion or incomplete fission— which is 

 in effect the same-of the ends of the chromosomes. Almost every 

 conceivable variety and modification of the typical ring is to be met 

 with depending on the region and extent of the fusion; Y-forms T- 

 forms, solid rods, crosses and V's, have all been found. The ring-form 

 is the type and from it all others of these varieties may be derived by 

 the increase of the fused area. Rings and their modifications are found 

 almost constantly in the large majority of forms, with or without tetrad 

 formation, in the first division of the spermatocyte. The more excep- 

 tional forms derived from it. while rarer, yet occur also in the first 

 division of the spermatocyte. Thus, Griffin found in Thalassema, 

 Y-forms, rod-forms, and X-forms; van der Stricht found in Tkijsanozoon 

 rod-forms with gradations of fusion modified from the ring-form; 

 v. Klinckowstrom, ring-forms, cross-forms, and rod-forms in the Plana- 

 rian, Prostliecermis. Many o,ther instances of excessive fusion m 

 the chromosomes of the spermatocyte of the first order might be given 

 in both animals and plants; e. g., Belajeff, 92, Atkinson, 99. 



Fusion of the daughter-chromosomes in their middle instead of at 

 the end produces the characteristic X- and +-forms, when they are 

 more or less V-shaped, and as the fusion extends out on the legs of the 

 V- Y- and T-forms as well. These have also been found in the divisions 

 of 'the spermatocyte in a number of forms, and usually in the division 

 of the spermatocyte of the second order rather than in the previous 

 mitosis. Thus, by van der Stricht in Thijsanozoon; by v. Klinckowstrom 

 in Prosthecemus; in Cyclops by Haecker; by myself in Desmognathus. 

 Among plants crosses were found in Larix by Belajeff, in Hemerocalhs 

 by Juel. In Allium, Ishikaua reports the X-formation by fusion of the 

 daughter-chromosomes at their apices in the first division; while in the 

 second division, the chromosomes unite by their ends to form rings, 

 there being thus a reversal of the condition found by me in Desmog- 

 nathus, which is perhaps more typical. Crosses may, therefore, be 

 formed as a modification of the end fusion (ring-formation), or by the 

 center (apex) fusion of the daughter-chromosomes. These two forms- 

 and X— seem to be the types from which other varieties of chromo- 

 some form in the spermatocyte are derived. 



In tetrad-formation, based on the ring-formation, the tendency toward 



