. The biological problem of today : preformation or epigenesis? The basis of a theory of organic development. Heredity. orphism and polymorphism. These seem to me V to show how very different final results may grow from identical rudiments, if these, in early stages /* of development, be subjected to different external « /• influences. Finally, I have a little to say about the sexual dimorphism that occurs so generally in the animal kingdom. Nearly all kinds of animals appear as male or 'as females. These differ from each other not only in that they produce eggs or spermatozoa, but frequently
. The biological problem of today : preformation or epigenesis? The basis of a theory of organic development. Heredity. orphism and polymorphism. These seem to me V to show how very different final results may grow from identical rudiments, if these, in early stages /* of development, be subjected to different external « /• influences. Finally, I have a little to say about the sexual dimorphism that occurs so generally in the animal kingdom. Nearly all kinds of animals appear as male or 'as females. These differ from each other not only in that they produce eggs or spermatozoa, but frequently in a number of more or less striking characters affecting different parts of the body, and known as secondary sexual characters. In fact, the difference between the sexes may be so great that a systematic naturalist, unacquainted with the mode of development of the creatures, might place them in different species, genera, or even families, on account of the striking differences in external characters. As an instance, take Bonellia, a gephyrean, the strange case of which has been remarked upon by Hensen and by Weismann. The male is about a hundred times smaller than the female, in the respiratory chamber of which it lives as a kind of parasite, and appears, so far as outward shape goes, more like a turbellarian than a gephyrean. None the less, male and female are alike not only while they are in the egg, but as larvse, and it is only towards the period of sexual maturity that the great difference between them begins to appear. So also is it with the dwarf males of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hertwig, Oscar, 1849-1922; Mitchell, P. Chalmers (Peter Chalmers), Sir, 1864-1945. New York, The Macmillan co
Size: 1344px × 1859px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorhertwigoscar18491922, booksubjectheredit, bookyear1900
