77 



The figures are taken from the l^t pollen-mother-celi division in plants and from 

 the spermatocytes of Triton. 



The series 1 — 17 refer to plants, la — 12a refer to plants; e in both series marks the 

 primitive extremities of the chromosomes. 



Series 1. Plants. 



Fig. 1. Nucleus with early stage in the longitudinal splitting of the linin. 



Fig. 2. Nucleus with young chromosomes. 



Fig. 3. Three types of chromosomes. Same stage as Fig. 2. 



Fig. 4. Typical mode of attachment of the elliptical chromosome to the spindle fibres. 



Fig. 5. Polar view of the same when still more bent; Fig. 5,, Diagrammatic re- 

 presentation of the same. 



Fig. 6. The opening of the ellipse along the spindle-fibres. 



Fig. 7. More advanced stage of the same. 



Fig. 8. The same showing the splitting into the two daughter-chromosomes. 



Fig. 9. An elliptical chromosome attached to the spindle near one end. 



Fig. 10. The same opening out along one end. 



Fig. 11. The same as in Fig. 10, but the chromosome attached a little nearer its 

 middle point. This form is also produced in cases where the longitudinal splitting 

 extends through the entire length of the chromosome. 



Fig. 12. One of the modes of attachment to the spindle of twisted elliptical 

 chromosomes. 



Fig. 13, 14 and 14^. Further developmental stages of the same. 



Fig. 15. A chromosome open at one end, with the limbs crossing each other. 



Fig. 16. Further stage of the same. 



Fig. 17. Chromosome open at both ends, the longitudinal halves twisted round 

 each other twice. 



Series 2. Animals. 



Fig. la. Nucleus in synaptic phase (c f. Fig. 1). 



Fig. 2a. Formation of young chromosomes (c f. Fig. 2). 



Fig. 8a. Relation of chromosomes to young spindle. 



Fig. 4a. Typical mode of attachment of the elliptical chromosome to the spindle 

 fibres. 



Fig. 5a. The opening of the ellipse along the spindle fibre». 



Fig. 6a. Widely opened elliptical chromosome, partly fused at one end. 



Fig. 7a. Later stage of the same. 



Fig. 8a and 9a. Modification in the normal mode of splitting of the loop (the 

 normal method is that shewn in Fig. 7 and 8 for plant cells). 



Fig. 10a. One of the modes of attachment, to the spindle, of twisted elliptical 

 chromosomes. 



Fig. 11a. A chromosome open at one end with the limbs crossing each other. 



Fig. 12a. A chromosome with one abnormally large hump at one end. 



still further back, whilst the point of their mutual attachment at the 

 equator of the spindle becomes tightly twisted or kinked, and even- 

 tually gives the observer the impression of its having been wrenched 

 in two (see Fig. 14 — 16). Sometimes the ends of the chromosomes 

 where they have just broken asunder are seen to be connected by 

 a filament, as though the viscous mass were being drawn out previous 

 to its final rupture. 



Finally, in those forms in which the primitive twist has been 

 more complete (Fig. 17), the chromosome seems usually to go through 

 the same changes as if it had assumed the elliptical form closed at 

 both ends, or else it may lie in the equatorial plane of the spindle 



