The Physiology of Twinning

The Physiology of Twinning

The Physiology of Twinning

The Physiology of Twinning

Excerpt

Since The Biology of Twins was written much new light has been thrown on the nature and causes of twinning and perhaps the dearest analysis of the fundamentals of twinning has been obtained through the experiments of the present writer on the eggs and embryos of the Pacific Coast starfish, Patiria miniata. It was felt that an experimental analysis of twinning was almost impossible in the case of mammals and it was therefore decided to make use of some species whose development was well known to be simple, readily controlled, and capable of easy observation. One would naturally select for such work either the bony fishes or the echinoderms: two groups which for a long time have been favorite materials for experimental biology. The echinoderms were chosen in preference to the fishes partly because the processes of cleavage and gastrulation are simpler and less open to controversy. For a long time I have felt that twinning was intimately associated with the process of gastrulation and on that account it seemed wise to study twinning in a form in which this whole process is so nearly diagrammatic.

When I went to the Pacific Grove laboratory in the spring of 1920, one of my chief concerns was to study experimentally the process of twinning in some echino-

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