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Μ. J. D. WHITE
tions and the range of habitats occupied by them needs to be considered
historically. Thus "peripheral" populations of a species whose range is
contracting may be expected to differ in composition from those of a
form whose distribution is expanding at the present time.
Although comparative animal cytotaxonomy is more developed than
some authors have been willing to admit, there are many lines along
which further research would be profitable. A much more complete picture of the occurrence of various types of adaptive cytological polymorphism, in all groups of organisms, needs to be built up. We are, for
example, almost totally ignorant as to whether such mechanisms exist,
and if so to what extent, in the groups with male haploidy and various
other kinds of aberrant chromosome cycles. We are also badly in
need of critical studies on induced and spontaneous rearrangements in
organisms with polycentric chromosomes or whose chromosome structure
is anomalous in other ways. The modern genetic analysis of evolution
extends all the way from chemical studies on the submicroscopic structure of chromosomes to ecological work on the dynamics of natural populations. But in all these studies we must not lose sight of the time dimension. The species of the present owe their cytogenetic constitutions
to historical processes, and no explanation of them which is solely in
terms of adaptation to the world of the present can be entirely satisfactory.
REFERENCES
Aeppli, E. 1952. Natürliche Polyploidie bei den Planarien Dendrocoelum lacteum
(Müller) und Dendrocoelum infernale (Steinmann). Z. indukt. Abst. u.
Vererbungsl 84: 182-212.
Bauer, H. 1945. Chromosomen und Systematik bei Chironomiden. Arch. Hydrobiol. 40: 994-1008.
Bauer, H. 1947. Karyologische Notizen. I. Über generative Polyploidie bei
Dermapteren. Z. Naturforsch. 2b: 63-66.
Bayreuther, K. 1954. Die Chromosomen der Flöhe (Aphaniptera). Naturwissenschaften 41: 309.
Beermann, W. 1956. Inversions-heterozygotie und Fertilität der Männchen von
Chironomus. Chromosoma 8: 1-11.
Bovey, R. 1948. Un type nouveau d'hétérochromosomes chez un mammifére: le
trivalent sexuel de Sorex araneus L. Arch. Julius Klaus-Stift. Vererbungsforsch.
Sozialanthropol. u. Rassenhyg. 23 : 507-510.
Cain, A. J., and Sheppard, P. M. 1954. The theory of adaptive polymorphism.
Am. Naturalist 88: 321-326.
Callan, Η. G. 1949. Chromosomes. New Biol. 7: 70-88.
Callan, Η. G., and Spurway, H. 1951. A study of meiosis in interracial hybrids of
the newt, Triturus cristatus. J. Genet. 50: 235-249.
Cámara, A. 1954. Advances in the centromere's problem. Proc. 9th Intern. Congr.
Genet. (Bellagio) 1:254-271.
Μ. J. D. WHITE
tions and the range of habitats occupied by them needs to be considered
historically. Thus "peripheral" populations of a species whose range is
contracting may be expected to differ in composition from those of a
form whose distribution is expanding at the present time.
Although comparative animal cytotaxonomy is more developed than
some authors have been willing to admit, there are many lines along
which further research would be profitable. A much more complete picture of the occurrence of various types of adaptive cytological polymorphism, in all groups of organisms, needs to be built up. We are, for
example, almost totally ignorant as to whether such mechanisms exist,
and if so to what extent, in the groups with male haploidy and various
other kinds of aberrant chromosome cycles. We are also badly in
need of critical studies on induced and spontaneous rearrangements in
organisms with polycentric chromosomes or whose chromosome structure
is anomalous in other ways. The modern genetic analysis of evolution
extends all the way from chemical studies on the submicroscopic structure of chromosomes to ecological work on the dynamics of natural populations. But in all these studies we must not lose sight of the time dimension. The species of the present owe their cytogenetic constitutions
to historical processes, and no explanation of them which is solely in
terms of adaptation to the world of the present can be entirely satisfactory.
REFERENCES
Aeppli, E. 1952. Natürliche Polyploidie bei den Planarien Dendrocoelum lacteum
(Müller) und Dendrocoelum infernale (Steinmann). Z. indukt. Abst. u.
Vererbungsl 84: 182-212.
Bauer, H. 1945. Chromosomen und Systematik bei Chironomiden. Arch. Hydrobiol. 40: 994-1008.
Bauer, H. 1947. Karyologische Notizen. I. Über generative Polyploidie bei
Dermapteren. Z. Naturforsch. 2b: 63-66.
Bayreuther, K. 1954. Die Chromosomen der Flöhe (Aphaniptera). Naturwissenschaften 41: 309.
Beermann, W. 1956. Inversions-heterozygotie und Fertilität der Männchen von
Chironomus. Chromosoma 8: 1-11.
Bovey, R. 1948. Un type nouveau d'hétérochromosomes chez un mammifére: le
trivalent sexuel de Sorex araneus L. Arch. Julius Klaus-Stift. Vererbungsforsch.
Sozialanthropol. u. Rassenhyg. 23 : 507-510.
Cain, A. J., and Sheppard, P. M. 1954. The theory of adaptive polymorphism.
Am. Naturalist 88: 321-326.
Callan, Η. G. 1949. Chromosomes. New Biol. 7: 70-88.
Callan, Η. G., and Spurway, H. 1951. A study of meiosis in interracial hybrids of
the newt, Triturus cristatus. J. Genet. 50: 235-249.
Cámara, A. 1954. Advances in the centromere's problem. Proc. 9th Intern. Congr.
Genet. (Bellagio) 1:254-271.