88 THE EVOLUTION OF SEX. 



(a) As early as 1849 Owen noted that, in the developing germ, 

 it was possible to distinguish between cells which became much 

 changed to form the body, and cells which remained little changed 

 and formed the reproductive organs. This view, as Brooks points 

 out, he unfortunately afterwards departed from in his "Anatomy of 

 the Vertebrates." 



(b) In 1866 Haeckel connected reproduction with discontinuous 

 growth, and insisted upon the material continuity between parent and 

 offspring. Somewhat later, both he and Rauber drew a clear contrast 

 between the somatic and reproductive elements, between the "per- 

 sonal" and "germinal" portions of the embryo, or between the body 

 and the sex-cells. 



(c) W. K. Brooks, in 1876 and 1877, again drew attention to 

 this significant contrast. 



(d) Yet more explicit, in 1877, was the ingenious Dr. Jager, now 

 better known in a very different connection, and a few of his sentences 

 well deserve to be quoted. Referring to a previous paper, he writes 

 as follows: "Through a great series of generations, the germinal pro- 

 toplasm retains its specific properties, dividing in every reproduction 

 into an ontogenetic portion, out of which the individual is built up, 

 and a phylogenetic portion, which is reserved to form the reproductive 

 material of the mature offspring. This reservation of the phylogenetic 

 material I described as the continuity of the germ-protoplasm. Encap- 

 suled in the ontogenetic material, the phylogenetic protoplasm is 

 sheltered from external influences, and retains its specific and embry- 

 onic characters." 



(e) In an exceedingly clear manner, to which sufficient attention 

 seems hardly to have been accorded, Galton, in 1876 and at other dates, 

 as again more indirectly in his recent "Natural Inheritance," drew 

 attention to the contrast between the gemmules of the ovum (stirp) 

 which go to form the body, and those which, remaining undeveloped, 

 form the sex-cells. " The developed part of the stirp is almost sterile," 

 (that is, without influence in heredity); "it is from the undeveloped 

 residue that the sexual elements are derived. 



(/") Lastly, in 1880, Nussbaum, in an elaborate investigation on 

 the differentiation of the reproductive cells, drew emphatic attention 

 to some cases of their early separation, and reasserted Jager' s concep- 

 tion of a continuity of germ-protoplasm. In this survey, however, 

 we do not pretend to decide the difficult question of priority in the 

 enunciation of this conception. Like many other generalizations, it 

 appears to have arisen all but simultaneously in many minds. 



IX. Weismann's Theory of the Continuity of the Germ- 

 protoplasm. — In some cases referred to in a foregoing paragraph, 



