Metamorphoses of man and the lower animals / by A. de Quatrefages ; translated by Henry Lawson.

Date:
1864
Catalogue details

Licence: Public Domain Mark

Credit: Metamorphoses of man and the lower animals / by A. de Quatrefages ; translated by Henry Lawson. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    This is what Herold saw,* and what had been also observed by Siebold. Let us suppose that—accident- ally in some species_, normally in others—the vital energy of the ovum is unusually intensified; then this ovum will become capable of producing by itself alone a complete animal, and we shall have partheno- genesis in all its stages, such as it is in the silkworm and the other species we have spoken of. Seen from this point of view, parthenogenesis, it is true, is not explained, but at all events it is associated with other jphenomenay and that alone allows us to go a step further. Fundamentally, and from the period of the germinal vesicle condition,t the corpuscle which will eventually become the ovum is formed by the same process as that which gives rise to the bud. Both result from the accumulation at a given point of a certain quantity of plastic material, abstracted from a pre-existing individual. Both owe their first origin to ^process of groiutJi. Now, we have said already that the growth of a living being cannot be indefinite. This is why re- jyrocl'itrtion hi/ hiuls exhausts itself or is arrested. Re]jvo chid ion by luifee undated ova should also have a limit. Here the great importance of the male sex makes itself apparent. But before the reader can grasp the * DisquisitionesdeAnimalium Yertebris carentiuni in ovo For- matione. 1838. t In my memoirs on the embryogeny of Herniella and Teredo, I stated my reasons for believing that the germinal vesicle precedes all the other elements of the egg. I believe that in the commence- ment it is a homogeneous spherule devoid of an enveloping membrane. S