80 



way different from that given in Fig. 6a, certainly occurs at the 

 beginning of the spindle in these organisms. 



Another mode of variation is produced by the loop becoming 

 attached to the spindle more or less at one end as in Fig. 10 a. In 

 consequence of this one off-standing hump or process becomes enor- 

 mously enlarged (Fig. 12 a) as in the case of plants, and, just as 

 among Lilies, all stages in the suppression of one hump and the 

 enlargement of the other can be observed. 



When a chromosome attached at one end to the spindle divides, 

 it opens out along the spindle in the manner represented in Fig. 10 a, 

 and when this expanded portion has split transversely as in Fig. 11a 

 forms corresponding with those described as "incurved chromosomes" 

 by Miss Sargeant are formed. But in Triton it will be seen that 

 the basal portion of the loop in contact with the spindle is not in 

 the same plane as the hump (Fig. 12 a). 



Chromosomes which are not attached so near their ends but 

 which nevertheless exhibit unequal humping on the equatorial plane, 

 divide by a fission which appears first across the lesser hump; very 

 often, but not always, the loop then opens out into the form which 

 was figured Taf. XXIV, 25 but not otherwise mentioned in Chap. IV 

 of Flemming's classical memoir i). 



There is also another modification of this type in which the long 

 sides of the elliptical chromosomes become closely approximated, the 

 chromosome dividing as a more or less rod-like body in which the 

 initial opening of the ring is barely visible (Figs. 8, 9). 



The last and most abnormal form of chromosome which we have 

 observed in these spermatocytes corresponds to that twisted figure 

 oftener seen in the case of Lilies, in which the chromosome ultimately 

 becomes drawn out as is represented in Figs. 10 a, 11a. 



These results obtained from animal and plant cells respectively 

 agree so closely, even in the most minute details, that it seems im- 

 possible to doubt that the entire process of heterotype mitosis is 

 essentially the same in both kingdoms. We leave it however an open 

 question whether this identity is due to phylogenetic causes, or whether 

 it is the expression of physical forces which, at corresponding periods, 

 operate under similar conditions. 



1) Neue Beiträge zur Kenntnis der Zelle. Aroh. f. mikr. Anat., 

 Bd. 29, 1887, p. 403. 



