Evolution, or Epigenesis?

Abstract

IN the English translation of Prof. Hertwig's book “The Cell,” it is stated (p. 295), “When the female gamete of the Alga Ectocarpus comes to rest, for a few minutes it becomes receptive. If the egg is not fertilised at this time … parthenogenetic germination begins to make its appearance … It may be accepted as a law of nature (italics mine) for mammals, and for the majority of other organisms, that their male and female sexual cells are absolutely incapable of development by themselves.” Thus, what occurs in the lower organisms is no criterion of what occurs in the higher, and vice versâ. Then why does Hertwig remark (p. 348), “It is quite sufficient for our purpose to acknowledge, that in the plants and lower animals, all the cells which are derived from the ovum contain equal quantities of the hereditary mass.… All idioblasts must divide and must be transmitted to the daughter-cells, in equal proportions both as regards quality and quantity” (italics mine). According to the above, it is “quite sufficient” for Hertwig's purpose of discrediting Weismann's contention for differentiated distribution of hereditary elements among somatic cells, to show that there is undifferentiated distribution in the case of plants and lower animals. But, reverting to the earlier quotation, if it is not sufficient to prove sexual reproduction in the case of the higher organisms, in order to disprove parthenogenesis in the case of the lower organisms, why should it be “quite sufficient,” in order to disprove distribution through germ-cells, in the case of the higher organisms, to show that, in plants and the lower animals one cell contains the same hereditary constituents as another? It is permissible to infer that differentiation in regard to germ-cells, in the higher animals, is no more disproved by the assumed demonstration that, in plants and the lower animals, there is no such differentiation, than that asexuality in lower is disproved by sexuality in higher organisms. Weismann, in my opinion, has proved to rational satisfaction that differentiation of germ from other cells must occur in the higher organisms, and he has offered a rational explanation, conformable with the theory of germ-plasm, of the apparently summational distribution of hereditary elements through somatic cells. Until Weismann's position is seriously undermined, which, so far, is not even a likely contingency, we must decline to accept Hertwig's assumed demonstrations in regard to plants and lower animals as invalidating the theory of germ-plasm. Similarly, that environment may affect the hereditary character of a primitive organism is no more evidence that it may so affect a mammal, than sexuality in the latter is evidence against parthenogenesis in the former. On page 348 we are told: “Johannes Müller has raised the question, ‘How does it happen that certain of the cells of the organised body, although they resemble both other cells and the original germ-cell, can produce nothing but their like, i.e. cells which are (in-?) capable of developing into the complete organism? Thus epidermal cells can only, by absorbing material, develop new epidermal cells, and cartilage cells only other cartilage cells, but never embryos or buds.’ To which he has made answer: ‘This may be due to the fact that these cells, even if they possess the power of forming the whole, have, by means of a particular metamorphosis of their substance, become so specialised, that they have entirely lost their germinal properties, as regards the whole organism, and when they become separated from the whole, are unable to lead an independent existence.’” The above is simply a restatement of Weismann's doctrine regarding the origin of germ-cells. All cells which have not, as Müller states, “lost their germinal properties, as regards the whole organism,“ are Weismann's germ-cells.