DEGENERATE SEXUAL REPRODUCTION. 



169 



it is to develop at all; and a second minimum, which the ovum must 

 attain, if a female is to be produced." Abundant nutrition of the 

 ovum tends to parthenogenesis, producing male offspring, as the 

 lower stage; but if the second limit be attained, resulting in females. 

 In the opposite direction, if the ovum have fewer resources, it requires 

 to be fertilized. Females or males will again result according to 

 the state of the elements. If no fertilization occur, the dependent 

 ovum must of course die. Rolph is always suggestive, but he erred 

 in regarding the sex-elements too quantitatively, in missing the quali- 

 tative antithesis of sex, and the opposition observed in cell-division. 

 (d) Strasburger also lays emphasis, in a subtler and more technical 

 way, on nutritive conditions. " In the rare cases of parthenogenesis, 

 specially favorable nutritive conditions may counteract the lack 01 

 nuclear plasma." He notes three different ways in which this may 

 happen, and also inclines to believe that retention of polar globules 

 would favor parthenogenetic development. It is important to notice 

 how two naturalists, so very different in their manner of attacking a 

 subject as Rolph and Strasburger are, come to this conclusion at 

 least in common, that favorable nutritive conditions favor partheno- 

 genesis. All the cells in the body tend to multiply, the ova retaining 

 this power develop embryos. 



(c) Weismann has a peculiar right to be heard on the nature of partheno- 

 genesis. For not only has he been for many year's an investigator of the tiny 

 daphnids or water-fleas, but he has recently made the important discovery, 

 already noticed, that parthenogenetic ova extrude only one polar globule. 

 There has not been time yet to prove that this is an absolute fact, but the 

 probabilities are strong that it is. Before stating his theory, it is necessary 

 to remember that the "germ-plasma" of Weismann is a specific and essential 

 portion of the nucleus of ovum or sperm, part of which keeps up the continuity 

 of heredity, by passing intact into the reproductive cells of the next generation. 

 Besides this all-important "germ-plasma," the nucleus of the ovum contains, 

 according to Weismann, an "ovogenetic nuclear plasma," which is of no direct 

 importance in development, but is useful to the ovum simply as an ovum. It 

 is the substance which is supposed to have to do with the general upbuilding 

 of the egg-cell, with the accumulation of yelk, secretion of membranes, and 

 the like. 



" The first polar body implies the removal of the ovogenetic nuclear plasma, 

 which has become superfluous when the egg has attained maturity. The 

 second polar body, on the other hand, implies the removal of a portion of 

 the germ-plasma itself. This is so effected that the number of ancestral elements 

 (Ahnen-idioplasmai) which composes it is reduced to a half. A .similar reduc- 

 tion must also take place in the number of the male germ-elements. 



" Parthenogenesis occurs when the entire sum of the ancestral elements 

 persist in the nucleus of the ovum. Development by fertilization demands, 

 however, that half these ancestral elements must first be extruded from the 

 ovum, whereupon the remaining half, in uniting with the sperm nucleus, regains 

 the original number. 



