1905.] 



On the Synapsis in Amphibia. 



559 



At all events, when the gemini have been produced each chromatic rod 

 rapidly extends outwards along linin threads in the manner represented by 

 fig. 6. In this we soon get an appearance which would be quite easy to 

 misinterpret as a fission in a spirem were not the earlier stages of the process 

 present in the surrounding tissue. 



A somewhat later stage is represented in fig. 7, where it is seen that the 

 original components of the gemini are rapidly elongating out into loops or 

 polarised chromatic bands. Cells possessing the characteristics represented in 

 figs. 6 and 7, constitute, in fact, the only representative in Triton of the 

 strong synaptic contraction figure so conspicuous in many other forms of 

 animals and plants. At a later stage the gemini, although still clearly 

 visible, have so far elongated and moved from their original positions as to 

 give the appearance represented in fig. 9. 



This movement, which corresponds to the unwinding of the synaptic loops 

 in mammals and other forms, is seen to have reached a further stage in 

 fig. 8. Here the condition of the early coarse spirem stage is clearly fore- 

 shadowed, and by stages such as those represented in figs. 10 and 11 the 

 characteristic polarised loops of the late spirem figure become gradually 

 formed. 



It appears then that the polarised loops are produced by the growth and 

 elongation of the original gemini, and that consequently each loop repre- 

 sents two premaiotic chromosomes, which may be associated together at one, 

 or both, of their ends. In general, in Triton and elsewhere the chromo- 

 somes forming the loops remain connected together only by the ends which 

 originally lay towards the nuclear interior, the outer pair of ends abutting 

 upon some portion of the nuclear membrane, and always in the late stages of 

 the spirem figure becoming widely detached from each other. 



Stages in the formation of the individual loops and the mode of attachment 

 of the chromosomes together at the round ends of the loops can be seen in 

 figs. 9, 10, 11, and 12. 



From the original formation of the gemini until the production of the 

 spirem loops, figs. 10 and 11, the chromatin in each lateral component or 

 chromosome is seen to be in the form of irregular granules, and remains 

 scattered along a linin framework ; but at subsequent stages (figs. 12, 13, 

 and 14) these chromatin particles become arranged, or split as it were, 

 into two longitudinal rows, and the loops from this time onwards present 

 the characteristic split appearance represented in figs. 13, 14, 15, and 16. 

 In stages such as that given in fig. 14 every loop is completely divided 

 throughout its entire length, and the longitudinal halves of the thread may 

 divaricate from each other as far as is to be seen in portions of the loops 



