The problem of age, growth, and death; a study of cytomorphosis, based on lectures at the Lowell Institute, March 1907 . f animals and has been recorded by hundreds ofobservers. It has hitherto attracted very little at-tention and despite the constancy and universality ofthe phenomenon no special significance has been at-tributed to it, I emphasised the constancy of thephenomenon in 1890 in an address delivered beforethe American Association for the Advancement ofScience. ^ Since then Richard Hertwie has been theonly author to lay special stress on the fact, but hefails to make the interpretat
The problem of age, growth, and death; a study of cytomorphosis, based on lectures at the Lowell Institute, March 1907 . f animals and has been recorded by hundreds ofobservers. It has hitherto attracted very little at-tention and despite the constancy and universality ofthe phenomenon no special significance has been at-tributed to it, I emphasised the constancy of thephenomenon in 1890 in an address delivered beforethe American Association for the Advancement ofScience. ^ Since then Richard Hertwie has been theonly author to lay special stress on the fact, but hefails to make the interpretation, which I shall offeryou in a few moments. We can get a further notion of the nuclear increaseby studying the very early development of a salaman-der (Fig. 59). Here upon the screen is the of asalamander, No. i. It represents really but a singlecell. It then divides into two cells : each of thosecells has a nucleus which we cannot see because these 1 Froc. A. A. A. S., xxxix. 164 AGE, GROWTH, AND DEATH pictures are taken from the living Qgg, and the livingegg is not transparent. Here (No. 4), it is dividing. Fig. 59. Amblystomnm piinciatwii. Progressive Segmentation of the , unsegmented ovum; 9, advanced segmentation.—After A. C. Eycleshymer. into four, here (No. 5), the upper portion of the fourcells has been split off, and we have seven cells showing DIFFERENTIATION AND REJUVENATION 165 In the figure, and an eighth on the back. Here (No. 9)the number of cells has increased very much. As youview these figures you will notice that they look verymuch indeed like oranges divided into segments. Itseems, in fact, as if this &gg, which was spherical inform, were being divided up into a certain number ofsegments. The process was first observed in the eggsof some of the amphibia (frogs, toads and salaman-ders), and it was therefore called segmentation, becauseit was not known at that time what the process reallymeant. We have then before us an ovum and a seriesof stage
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