296 THOS. H. MONTGOMERY, 



stage joiniog the central ends of every two chromosomes is a clearly 

 marked linin fibre ; this I believe from these considerations is the per- 

 sisting longitudinal half of an inter-chromosomal fibre of the monaster 

 stage. If this be so then such a fibre must have remained continuously 

 from the monaster stage as the connection between the central ends 

 of two daughter chromosomes, and this is very probably the case. 

 By the contraction of such a persisting linin fibre could be very well 

 explained, accordingly, the union into pairs, by a pulling together of 

 the central ends of the chromosomes, of the daughter chromosomes, 

 which would be at the same time an explanation for the mechanics 

 of the reduction in number of the chromosomes. 



The diagrams 257 to 259, Plate 25, illustrate this point. Fig. 257 

 shows a spirem stage, in which for the sake of clearness only 4 

 chromosomes are shown ; the linin spirem is in red. Compare with this 

 Figs. 7, 10 and 13 of Plate 19, where a portion of the persisting 

 linin thread is plainly seen, but in which most of the thread cannot 

 be seen owing to its position outside of the plane of the section. 

 Diagram 258 represents a monaster stage, with the linin spirem shown ; 

 compare Figs. 16, 28, 32 and 33 of Plate 19 for actually observed 

 cases of the persisting spirem thread in this stage. Up to this stage 

 there can be no doubt of the persistence of the continuous linin 

 spirem, and when it can not be seen in every case it is apparently 

 because the chromosomes which it connects do not lie exactly in the 

 plane of the section. Diagram 259 represents the metakinesis of 4 

 chromosomes; compare Figs. 40 to 47 of Plate 19. In the latter 

 figures the only portion of the linin thread which still seems to per- 

 sist is in the form of connective fibres. But though I have been 

 unable to see the other portions of the spirem in this stage, I hold 

 that they persist continuously and divide, for reasons given above, 

 namely that they are clearly apparent in preceding and in subsequent 

 stages. Diagram 259, therefore, is not based upon observed pheno- 

 mena, but is a subjective representation of the relations of the linin 

 and chromatin in the stage between the stages shown in diagram 258 

 (spermatogonic monaster) and in diagram 260 (synapsis). I would 

 explain the difficulty of observing the linin threads in the metakinesis, 

 by the assumption that they probably become stretched and so more 

 attenuated in this stage ; other difficulties are the comparative scarcity 

 of these metakineses, and the dense grouping of the chromosomes 

 which would seem to hide the portions of the linin spirem. 



The relations of the linin, as represented in diagram 259, are 



