555 



On the Synapsis in Amphibia. 



By J. E. S. Moore, A.B.C.S.,F.L.S., Director of the Cancer Besearch 

 Laboratories, University of Liverpool, and Miss A. L. Embleton, B.Sc. 



(Communicated by J. Bretland Farmer, F.B.S., F.L.S. Beceived December 5, 

 1905,— Bead January 18, 1906.) 



[Plates 20—23.] 



In 1903 and 1904 one of us, in conjunction with Professor Farmer, 

 described the maiotic process in a variety of animals and plants.* From the 

 observations then accumulated it was in the first place shown that what we 

 termed the maiotic process appears to be the same throughout the animal and 

 vegetable kingdoms. In the second it was pointed out that the general 

 scheme we were able to formulate was in accord with the particular descrip- 

 tion of the metamorphosis given by Korscheltt for Ophryotrocha as long ago 

 as 1895, as well as with the account of the same change in some amphibia 

 given by Montgomery! in the same year as ourselves. 



According to this conception of the maturation process, the reduction in the 

 number of chromosomes to one half is brought about by a pairing of somatic 

 chromosomes which takes place in the prophase of the first maiotic 

 (heterotype) divisions. In this way we have in some mammals, for example, 

 16 pairs of chromosomes in the place of 32 single elements. 



These chromatic gemini, as we propose to call them, go on to the spindle 

 in the same way as ordinary premaiotic or somatic chromosomes. But 

 during the division each of the respective gemini separate into the two 

 component parts ; so that in the cases of mammals above referred to there 

 are 16 premaiotic chromosomes distributed to each daughter cell. 



According to this view it would appear that during the first maiotic 

 division no longitudinal fission of the chromosomes composing the gemini 

 comes into play, and the longitudinal split which is visible in the spirem 

 figure only effects that incomplete fission of the daughter elements first 

 observed by Flemming in the diasters of the first maiotic division in 

 amphibia (see fig. 22). 



In this way the longitudinal split of the thread which takes place in the 

 spirem stage only becomes completed and effective during the second 



* Cf. Farmer and Moore, 'Boy. Soc. Proc.,' May, 1903; Farmer and Moore, 'Quart. 

 Journ. Micros. Sci.,' vol. 48 ; Farmer and Shove, 'Quart. Journ. Micros. Sci.,' vol. 48 ; 

 Moore and Eobinson, ' Quart. Journ. Micros. Sci.,' vol. 48. 



t Korschelt, ' Zeitschr. fur Wiss. Zool.,' vol. 9. 



X Montgomery, ' Biol. Bull.,' vol. 4, 1903. 



VOL. LXXVII. — B. 2 S 



