563 



On the Existence of Permanent Forms among the Chromosomes of 

 the First Maiotic Division in Certain Animals* 



By J. E. S. Moore, A.R.C.S., F.L.S., Director of the Cancer Research 

 Laboratories, University of Liverpool, and George Arnold. 



(Communicated by J. Bretland Farmer, F.B.S. Received December 13, 1905, — 



Read January 18, 1906.) 



[Plates 24 and 25.] 



Many cytological investigators have drawn attention to the peculiar 

 forms assumed by the heterotypical aggregates of chromosomes, or, as we have 

 lately termed them, the Synaptic Gemini} of the first maiotic division. It 

 was indeed the striking peculiarities presented by the forms assumed by 

 these bodies, and the comparative ease with which they can be distinguished 

 from the true chromosomes of pre- and post-maiotic mitoses, which led 

 Professor Farmer^ and one of us some years ago to make a list of the different 

 forms we encountered in different animals and plants. We utilised this 

 comparison in establishing what was at that time by no means clear, namely, 

 that in regard to the maiotic divisions we are dealing with an identical 

 process throughout both animals and plants. 



In the note referred to and in subsequent publications by other authors, 

 the view has been taken that the adult gemini (heterotype chromosomes) are 

 to be regarded as capable of assuming any of the forms which two flexible 

 rods can take. As for example, when bent round each other ; lying parallel 

 to each other ; associated together in the form of a cross ; joined end to end 

 in the form of a ring ; and so on. The rarer forms, such as tetrads, being 

 accounted for by supposing that the four-fold figure results from a thickening 

 or clubbing of the ends of the associated chromosomes thus : — = tt . In 

 many instances where tetrads are found this is undoubtedly the explanation 

 of their form. 



Thus the possible modes of association between two flexible rods, together 

 with the effects of alteration in their form, and the action of the spindle 

 fibres, have hitherto been regarded by ourselves and others as sufficient to 

 account for the great variety of aspect which the maiotic gemini are found 

 to present. 



* The title of the paper, as originally communicated and read, was " On the Constancy 

 of Form among the Synaptic Gemini (Heterotype Chromosomes) in Certain Animals." 



t Moore and Embleton, " On the Synapsis in Amphibia" (preceding paper). 



J Farmer and Moore, "On the Essential Similarities existing between the Heterotype 

 Nuclear Divisions in Animals and Plants," ' Anat. Anzeiger,' 1895. 



