Ryder.] 140 [May 16, 



need of immediately feeding, but which is enabled to reach a certain self- 

 helpful morphological complication before it begins the struggle for exist- 

 ence for itself. It provides a large cytoplasmic field in which rapidl}' re- 

 current successive and simultaneous karyokineses can take place under 

 the guidance of the inherited tendencies resident in the nucleoplasm and 

 cytoplasm of the combined germs. The one sex appears to supply the 

 field for segmentational activity, the other the segmentational impulse 

 itself. In other words, sexuality is the expression of the action of the 

 principle of the physiological division of labor, extended so as to involve 

 two kinds of individuals of the same species, or two different functionless 

 parts of the same individual, as in hermaphrodites. 



There is no convincing evidence that the male induces variability. The 

 argument from hybrids is of little value. The tendency to an equilibrium 

 as the consequence of close interbreeding or of continued promiscuous 

 interbreeding is the same, and is to be interpreted as the result of the 

 constancy of the mode of growth of the average individual which must 

 finally result, following from the average of hereditary characters which 

 are finally thus transmissible. As soon as slightly differing forms are 

 crossed the karyokinetic equilibrium is disturbed and variability ought on 

 a priori grounds to ensue. To saddle the induction of variability upon 

 the male does not seem to be demonstrated, as the factors involved are too 

 numerous to enable us to decide what ones are important and what are 

 unimportant. 



A view which has far more in its favor is that a large oosperm, inter- 

 preted as above, with a large cytoplasmic field, is inherently more liable 

 to vary its karyokinetic processes through very slight variations in the ex- 

 ternal influences than a small or a parthenogenetic one. That sexuality, 

 taken in the widest sense, is responsible for variability is probably nearer 

 the truth. That the oosperm, with its large cytoplasmic field, is the real 

 arena in which variability disports itself, may be taken for granted. It is 

 also very evident that the evidence derived from the development of 

 monsters is clearly in favor of such a view. Monsters are developed only 

 when the early stages of development are karyokinetically disturbed, as 

 is well known. Moreover, there is no hard and fast line between mon- 

 strosities and variations of a less and less monstrous character until those 

 of an almost imperceptible and unimportant character are encountered. 

 That the tendency towards variability is more marked in the young than 

 in the adult stages of fixed and slightly variable types of Metazoa may be 

 regarded as a truism, and must be considered the foundation of these 

 views. 



In that temperature affects the rate of karyokinetic processes, it is clear 

 that inequalities of temperature simultaneously affecting different points 

 on the surface of an egg would affect the rate of segmentation of the 

 cells of such different points and thus induce variability. A single karyo- 

 kinesis disturbed or impeded on one side of an embryo must disturb all 

 subsequent ones. A mechanism so delicate as this of karyokinesis may 



