;5i) 



formation from that composing the ordinary, but not yet greatly modi- 

 fied, cells of the body. Dr. AVeismann, on the other hand, maintains 

 that the egg, or more exactly the nucleus of the egg, contains a substance, 

 his germ-plasm, which possesses a peculiar chemical, and more especially 

 molecular, structure, and which is the bearer of " the whole of the inher- 

 ited tendencies of development." In the process of the development of 

 the embryo, not all of this germ plasm is consumed in the construction 

 of the body ; but a small portion is set aside and remains in the body of 

 the embryo unchanged, and destined to enter at the end into the forma- 

 tion of the eggs which shall give being to the next generation. The ma- 

 terials of the body cells Weismann calls somatoplasm, to distinguish it from 

 the germ-plasm. The germ-plasm, although borne about in the body of 

 the organism that in time will produce offspring, and though nourished 

 by its somatoplasm, is whollj^ distinct from the latter, and is very slightly 

 if at all affected by it. Weismann says of it: " The germ-plasm, or idio- 

 plasm of the germ-cell, certainly possesses an exceedingly complex min" 

 ute structure, but it is nevertheless a substance of extreme stability, for 

 it absorbs nourishment and grows enormously without the least change 

 in its complex molecular structure." Weismann even maintains that 

 this reproduction of the germ plasm without change may go on for thou- 

 sands of years. He has compared the germ- plasm to a creeping root- 

 stock which at intervals sends up a vigorous shoot. The shoot flourishes 

 for awhile and dies, but the rootstock survives, to produce other shoots 

 in indefinite number. The germ-plasm enjoys a sort of immortality. 



The cause of heredity has always been a mystery. How is it that a 

 cell which has not the slightest resemblance to the animal that produced 

 it can go through a complicated series of divisions and transformations 

 and at last gradually, but unerring!}^, reproduce even to minute details 

 the structure and foim of the pai'ent ? How is it that two eggs, indistin- 

 guishable from each other, but laid by difi"erent animals, developing per- 

 haps under identical circumstances, can reproduce exact copies of their 

 respective parents? Darwin attempted to give an explanation by assum- 

 ing that each cell of any organism emits minute particles, called by him 

 gemmules, which enter the germ-cells and become there representatives of 

 the cells of the whole body. The germ-cells must according to this the- 

 ory contain millions of gemmules. When development of the egg occurs 

 the contained gemmules determine the reproduction of their respective 

 cells in due order of time, place, and form. When any part of the body 



