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And he was just observing that newts differ from salamanders in the shape of the tail, which is compressed, and that a marked sexual dimorphism prevails in most species, when the young lady rose and said that she thought she would go back to the house." "And then " "She went, sir." I stood musing.
The consideration of these facts on dimorphism, as well as of the results of reciprocal crosses, clearly leads to the conclusion that the primary cause of the sterility of crossed species is confined to differences in their sexual elements.
Granting these conclusions, monstrosities on the one side, and dimorphous wild species on the other, constitute the most striking examples of the inheritance of latent characters. The bearing of the phenomena of dimorphism upon the principles of evolution formulated by Lamarck, and modified by his followers to constitute Neo-Lamarckianism, remains to be considered.
It will be seen that although in the progeny of this mating all the grossulariata were males and all the lacticolor females, yet this case is by no means similar to that of sexual dimorphism in which the characters are normally always confined to the same sex. For the lacticolor character in the parent was in the male, while in the offspring it was in the female. Univ.
MacLachlan, R., on Apatania muliebris and Boreus hyemalis; on the anal appendages of male insects; on the pairing of dragon-flies; on dragon-flies; on dimorphism in Agrion; on the want of pugnacity in male dragon-flies; colour of ghost-moth in the Shetland Islands.
I had noticed in 1838 or 1839 the dimorphism of Linum flavum, and had at first thought that it was merely a case of unmeaning variability. But on examining the common species of Primula I found that the two forms were much too regular and constant to be thus viewed.
The Mendelian merely sees a relation of the character to sex, but overlooks entirely the question of the dimorphism in the original species from which the domesticated breeds are descended.
Individuals of the same species often present, as is known to every one, great differences of structure, independently of variation, as in the two sexes of various animals, in the two or three castes of sterile females or workers among insects, and in the immature and larval states of many of the lower animals. There are, also, cases of dimorphism and trimorphism, both with animals and plants.
According to T. H. Morgan, it is simply due to the fact that the determinants for such characters are situated in the sex-chromosome. Morgan, however, also states that a case of true sexual dimorphism arose as a mutation in his cultures of Drosphilia. The character was eosin colour in the eye instead of the red colour of the eye in the original fly.
In the Staphylinidae, the horns of the males are extraordinarily variable in the same species, just as we have seen with the Lamellicorns. In Siagonium we have a case of dimorphism, for the males can be divided into two sets, differing greatly in the size of their bodies and in the development of their horns, without intermediate gradations.
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