PROFESSOR WEISMANN' S THEORIES. 483 



and multiply for many years after germ-cells have died out. If 

 similarly measured, then, these cells of the last class prove to be 

 more mortal than those of the first. But Prof. Weismann uses a 

 different measure for the two classes of cells. Passing over the 

 illegitimacy of this proceeding, let us accept his other mode of 

 measurement, and see what comes of it. As described by him, 

 absence of death among the Protozoa is implied by that unceasing 

 division and subdivision of which they are said to be capable. 

 Fission continued without end, is the definition of the immortality 

 he speaks of. Apply this conception to the reproductive cells in 

 a Metazoon. That the immense majority of them do not multiply 

 without end'we have already seen : with very rare exceptions they 

 die and disappear without result, and they cease their multiplica- 

 tion while the body as a whole still lives. But what of those ex- 

 tremely exceptional ones which, as being actually instrumental to 

 the maintenance of the species, are alone contemplated by Prof. 

 Weismann ? Do these continue their fissiparous multiplications 

 without end ? By no means. The condition under which alone 

 they preserve a qualified form of existence, is that, instead of one 

 becoming two, two become one. A member of series A and a 

 member of series B coalesce, and so lose their individualities. 

 Now, obviously, if the immortality of a series is shown if its mem- 

 bers divide and subdivide perpetually, then the opposite of im- 

 mortality is shown when, instead of division, there is union. Each 

 series ends, and there is initiated a new series, differing more or 

 less from both. Thus the assertion that the reproductive cells are 

 immortal, can be defended only by changing the conception of 

 immortality otherwise implied. 



Even apart from these last criticisms, however, we have clear 

 disproof of the alleged inherent difference between the two classes 

 of cells. Among animals the multiplication of somatic cells is 

 brought to an end by sundry restraining conditions ; but in vari- 

 ous plants, where these restraining conditions are absent, the 

 multiplication is unlimited. It may, indeed, be said that the 

 alleged distinction should be reversed ; since the fissiparous mul- 

 tiplication of reproductive cells is necessarily interrupted from 

 time to time by coalescence, while that of the somatic cells may 

 go on for a century without being interrupted. 



In the essay to which this is a postscript, conclusions were 

 drawn from the remarkable case of the horse and quagga there 

 narrated, along with an analogous case observed among pigs. 

 These conclusions have since been confirmed. I am much indebted 

 to a distinguished correspondent who has drawn my attention to 

 verifying facts furnished by the offspring of whites and negroes 

 in the United States. Referring to information given him many 



