On Dimorphism in the hymenopterous genus Cynips," "Proc.
I have been led lately from experiments (not published) on dimorphism to reflect much on sterility from hybridism, and partially to change the opinion given in "Origin.
I have just sent in a paper on Dimorphism of Linum to the Linnean Society (155/8.
If sexual dissimilarity is due to the tendency of the male to dissipate energy, why do we see very marked dimorphism in one species, and no dimorphism in a very nearly allied species?
Pictet has shown that the alternating wet and dry seasons in some tropical countries are the cause of, or stimulus that induces, seasonal dimorphism in some butterflies.
Sexual Dimorphism Many species of birds display what is known as seasonal dimorphism, still more display sexual dimorphism.
Cunningham makes an attempt to explain the phenomena of sexualdimorphism on Neo-Lamarckian principles.
Again, Cunningham is not correct in saying that sexual dimorphism is "virtually absent" in the Columbidae.
Few birds display so striking a sexual dimorphism as the Orange Dove (Chrysoena victor) of Fiji, in which the male is bright orange and the hen green.
The Four Kinds of Mutations It is our belief that sexual dimorphism arises frequently, if not invariably, as a mutation.
The result of maturation, as in the other species here described and in Tenebrio molitor, is dimorphism of the spermatozoa.
Mr. MacLachlan informs me of another instance of dimorphism in several species of Agrion, in which some individuals are of an orange colour, and these are invariably females.
Dytiscus, dimorphism of females of; grooved elytra of the female.
Shyness of adorned male birds; Siagonium, proportions of the sexes in; dimorphism in males of.
In the British Museum I noticed one male specimen of Siagonium in an intermediate condition, so that the dimorphism is not strict.
Wolfgang Ostwald has produced experimentally, through variation of temperature, dimorphism of form in Daphnia.
The tendency of the female to dimorphism and polymorphism has been of great importance in determining this predominance.
By seasonal dimorphism is meant the fact that species may appear at different seasons of the year in a somewhat different form or colour.
See also the previous essay “On the Seasonal Dimorphism of Butterflies,” pp.
It has been shown that the phenomenon of seasonal dimorphism has the same proximate cause as climatic variation, viz.
The origin of seasonal dimorphism appears to me to be against this view, howsoever seductive and grand the latter may seem.
From the investigations on seasonal dimorphism it appears that a cycle of generations can arise in an entirely different way.
Levana and the Pierinæ, the winter form is the primary one, so that the dimorphismproceeds from the said winter form and does not originate the winter but the summer form, as will be explained.
Sexual dimorphism in the position of the scar is characteristic of some snakes but is minimal in cottonmouths.
Funk were larger, and differences in the proportions of the tail length and snout-vent length suggest the sexual dimorphism found in larger individuals.
Bateson offers no explanation of this, but it obviously suggests that some trace of the original dimorphism of the sheep in this character was retained in both horned and hornless breeds.
Morgan, however, also states that a case of true sexualdimorphism arose as a mutation in his cultures of Drosphilia.
The Mendelian merely sees a relation of the character to sex, but overlooks entirely the question of the dimorphismin the original species from which the domesticated breeds are descended.
But as pointed out above, selection cannot explain the dimorphism in either case.
Many instances of this second form of dimorphism have been described under the name of alternation of generations.
The other kind ofdimorphism or polymorphism differs from the first in being the result of the differentiating action of external circumstances, not on the mature, but on the young individual.
I have since been informed by Mr. Trimen that this species does not conceal itself by day, so that the dimorphism may be regarded as a character retained from an earlier period and adapted to the present life conditions.
I was undoubtedly first led to this conception by the results which arose from my studies on the seasonaldimorphism of butterflies.
The above views on the nature of variability, which were also broadly expressed in the first essay “On the Seasonal Dimorphism of Butterflies” (pp.
Trimorphism and dimorphism in plants, papers on, 45.
Dimorphism and trimorphism in plants, papers on, 45.
The distinctive character therefore of dimorphismis this, that the union of these distinct forms does not produce intermediate varieties, but reproduces the distinct forms unchanged.
Dimorphism is thus seen to be a specialized result of variation, by which new physiological phenomena have been developed; the two should therefore, whenever possible, be kept separate.
Dimorphism of this kind in the animal kingdom does not seem to have any direct relations to the reproductive powers, as Mr. Darwin has shown to be the case in plants, nor does it appear to be very general.
Four days later, after the fourth ecdysis, the dimorphism becomes a polymorphism.
Interrogationis:-- The interesting experiments of Mr. Edwards are here principally introduced because they show how many weighty questions in connexion with seasonal dimorphism still remain to be solved.
Nevertheless, it cannot be denied that seasonal dimorphism occurs also in some species which do not hibernate as pupæ but as caterpillars; as, for instance, in the strongly dimorphic Plebeius Amyntas.
Seasonal dimorphism occurs also in moths, although I am not in a position to make a more precise statement on this subject,[6] as my own observations refer only to butterflies.
The species of Araschnia through which the discovery of seasonal dimorphism was made, formerly bore the two specific names A.
But even if seasonal dimorphism is to be ascribed to heterogenesis, it must by no means be asserted that those cases of cyclical propagation hitherto designated as heterogenesis are completely identical with seasonal dimorphism.
A seasonal dimorphism thus appears which is combined with ordinary dimorphism, winter and summer forms alternating with each other; but the first appears itself in two forms or varieties, vars.
Seasonal dimorphism has already been designated by Wallace as alternation of generation,[37] a term which cannot be disputed so long as it is confined to a regular alternation of dissimilar generations.
From the considerations offered, it thus appears that the phenomena of seasonal dimorphism may depend on extremely complex processes, so that one need not be surprised if only a few cases now admit of certain analysis.
Munier-Chalmas and Schlumberger brought out the fact of dimorphism in the group, which was later elucidated and incorporated in the full cytological study of the life-cycle of Foraminifera by J.
Two phenomena interfere with the ready availability of the characters of form for classificatory ends--dimorphism and multiformity.
The sexual dimorphism in the skull is slight, the skull of the male being only a third heavier than that of the female.
In Mustela frenata, the subspecies noveboracensis shows most sexualdimorphism in weight of skull (3.
There are, also, cases of dimorphism and trimorphism, both with animals and plants.
We first have dimorphism and heteromorphism, the phenomena of which have been already sketched in our seventh chapter.
Absence of sexual dimorphism in the Bell Vireo obviously suggests that behavioral criteria are used by the birds in sex-recognition.
Absence of sexual dimorphism suggests that behavioral criteria are used by the birds in sex-recognition; the male is dominant and the female is subordinate.
It constructs the same kind of nest and in similar situations; why then the sexualdimorphism in this species and in no other species?
Hence it might seem that, in the case of the sunbird, the above-mentioned explanation of the sexual dimorphism is the true one.
Weismann in his classical work on the Seasonal Dimorphism of butterflies (1876).
In tropical countries where instead of an alternation of winter and summer, alternate dry and rainy seasons prevail, somewhat similar seasonal dimorphism has been observed among many butterflies.
Thus, while the disintegration of the couple augments the feminine dimorphism, the diminution of the natural dimorphism renders the transformation of the couple more uneasy and more precarious.
Limited to the non-sexual elements, human dimorphismis very feeble.
The dimorphism of mammals is even less often favourable to the female than is that of birds.
In the true pheasant the dimorphism is still more marked.
Numeric dimorphism follows dimorphism of mass; the family of one sort of butterfly of the Marquesas Islands is composed of one male and of five females all different, so different that one long supposed them distinct species.
Dimorphism favourable to males: the oriole, pheasants, the ruff.
Woman's liberty also accentuates the dimorphism but by another process.
Only after serious study of sexual dimorphism in the animal series may one venture a few reflections on feminism.
The dimorphism of birds of paradise is even more marked than in the preceding cases.
In all cases where the dimorphism is slight, and is the direct consequence of the possession of sexual organs, castration inclines the male toward the female type.
Civilization has certainly accentuated the initial dimorphism of man and woman--at least unless one of the very conditions of civilizations be not precisely a notable difference, morphologic and psychologic, between the two sexes.
The sexual dimorphism displayed by the red turtle dove is a fact equally awkward for the Wallaceians, because the habits of this species appear to be in no way different from those of the other doves.
Mr. Cunningham evidently is not acquainted with the red turtle dove (Oenopopelia tranqebarica) so common in India, or he would not have asserted that sexual dimorphism is virtually absent in the Columbidae.
These facts, of themselves, are quite sufficient to disprove the theory that sexual dimorphism in birds is due to the hen's greater need of protection.
This species is of interest on account of the large amount of sexual dimorphism which it displays.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "dimorphism" in a variety of sentences. We hope that you will now be able to make sentences using this word.
