STUDIES OX CHROMOSOMES 
• 71 
usually outside the ring (as in fig. 2h) ; while the third 7n-chromosome 
is always coupled with the two others at the center of the ring, and 
moves to one pole without division. In the second division these 
relations are almost exactly reversed, the m-chromosome dividing 
equationally as a univalent, while the supernumerar}^ does not 
divide and is typically coupled with the idiochromosome bivalent 
near the center of the group. I desire to emphasize the fact that 
these differences are in no way obscure or difficult to see, but are 
conspicuously shown in so great a number of cells as to remove 
all doubt. ^ 
^This point demands emphasis because of the scepticism expressed by certain 
writers in regard to the constancy of the chromosomes in respect to number, size 
and behavior. Conspicuous among these writers is Delia Valle ('09) who has 
brought together a valuable if somewhat uncritical review of the literature, and 
contributes careful observations of his own upon variations in the chromosome- 
number in the somatic cells of Salamandra. Such scepticism is perhaps not sur- 
prising in view of the unlucky contradictions that still exist in the literature even 
of so favorable and well known a group as the insects. But to ascribe this con- 
fusion of the literature to a confusion of the facts — i. e., to an inconstancy so great 
as to preclude the possibility of attaining exact results — would be, I think, a fatal 
blunder. The confusion in the literature cannot, of course, be attributed altogether 
to mistakes of observation or to accidents of technique — though both these must 
be held to a strict reckoning. I am not aware that anyone has maintained that 
the relations of the chromosomes form an exception to all other biological phenom- 
ena in being absolutel}' fixed and immutable; and due weight should be given 
to the numerical variations that have been recorded by Delia Valle and many others 
myself included. The fact remains that it is possible to determine accurately 
what are the normal or typical relations of the chromosomes, as of other struc- 
tures, and to establish in many cases their high degree of constancy. The same 
common sense must be used in the treatment of these relations as in the case of 
other phenomena that are subject to variation. For example, insects have been 
seen with seven legs, but it is not for this reason to be doubted that insects have 
six legs. In like manner, in the ovaries of Largus cinctus I have seen as many as 
three dividing cells that show 13 chromosomes; but I nevertheless do not doubt, 
after the study of a large number of cases, that the typical number is 12. 
The case of Metapodius is disposed of by Delia Valle in the following easy fash- 
ion. "Not constancy but variability in the number of chromosomes is the general 
rule in all organisms; of which the observations published by him (Wilson) are 
but a special confirmatory case" {op.cit.,p. 161, translation). Better acquaintance 
with the facts in Metapodius would probably render Prof. Delia Valle less certain 
of this; for I am confident that no observer of ordinary competence could confuse 
such a series of relations as that here displayed with the occasional fluctuations 
with which we are familiar in many forms, including this very genus. 
