The problem of age, growth, and death; a study of cytomorphosis, based on lectures at the Lowell Institute, March 1907 . next moult the old shellor cuticle is cast off. Theminute study of this processhas shown that the regenera-tion depends practically ex-clusively upon the cells of theyoung type, and that afterthey have grown out and ac-cumulated here in this man-ner, No. 3, d, some of themundergo differentiation, be-coming muscle cells; otherschange in the manner indi-cated here, No. 4, where wesee a commencing alterationof the nuclei, which is furtheraccented in Fig. 71, and leads , . r , 1
The problem of age, growth, and death; a study of cytomorphosis, based on lectures at the Lowell Institute, March 1907 . next moult the old shellor cuticle is cast off. Theminute study of this processhas shown that the regenera-tion depends practically ex-clusively upon the cells of theyoung type, and that afterthey have grown out and ac-cumulated here in this man-ner, No. 3, d, some of themundergo differentiation, be-coming muscle cells; otherschange in the manner indi-cated here, No. 4, where wesee a commencing alterationof the nuclei, which is furtheraccented in Fig. 71, and leads , . r , 11 Fig. 71. Section through to such a groupmg of the cells ^ regenerating antenna of that the glands, which were C«?V<r«J.—After Ost. Advanced originally present there, are stage, in which the young new ^ ^ joint IS already shaped within the also reproduced. The regen- old shell, a, cicatricial tissue ; d, erative process, then, clearly regenerated tissue ; y. new joint; ,,, f. c«,cuticula(old shell). Magnified. illustrates to us, irom another point of view, the great importance of the young type of 2IO AGE, GROWTH, AND DEATH The eyes of crabs and related animals {Decapoda)are born on stalks. If these stalks are cut partly off soas to remove all of the eye, but leave part of thenervous centre (^ganglion) in the base of the stalk,it is found that in a considerable percentage of cases anew eye will be formed. Miss M. I. Steele^ has madea study of this regeneration. She states that thehealing over of the wound and the growth of theundifferentiated cells of the outer layer (ectodermor hypodermis) occurs much as just described forthe antenna of Oniscus. Later the hypodermal cellslose their primitive and simple character and bypassing through various but co-ordinated differen-tiations evolve new complete ommatidia^ as thestructural units are termed which constitute the eyein crabs and other Crustacea. It may interest you toknow that if the whole or nearly the whole eye
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectde, booksubjectoldage
