The phenomenon of seasonal dimorphism is of especial moment for the plankton dwellers.
Where the sexes are distinct, a more or less marked dimorphism often exists.
The iris is in most young birds at first brown or dull-coloured, but with maturity attains often very bright tints which add considerably to the charm of the bird; sexual dimorphism is in this respect of common occurrence.
After this a marked sexual dimorphism sets in.
Skua, is not known to exhibit the remarkable dimorphism to which the two preceding are subject.
In association with antimonious and arsenious sulphides, silver sulphide forms many important minerals, which sometimes present dimorphous forms, reflecting the dimorphism of silver sulphide; moreover, the corresponding arsenious and antimonious compounds are frequently isomorphous.
Cross pollination is often favoured by dimorphism of the flower, as shown in species of Primula (fig.
In some species of Dinophilus there is pronounced sexual dimorphism (the male being small and without gut) as in the Rotifera.
Molluscs are usually of separate sexes, but sexual dimorphism is seldom highly developed.
To allure and attract them to visit the flower the odoriferous secretions and gay colours are developed, and the position and complicated structure of the parts of the flower are adapted to the perfect performance of the process, It is comparatively rare in hermaphrodite flowers for self-fertilization to occur, and the various forms of dichogamy, dimorphism and trimorphism are fitted to prevent this.