Fertilization in the Fallopian tube or uterus is allowed to be possible, and it is admitted that, in exceptional cases, fertilization of the hen’s egg is possible so long as it is not surrounded by the shell-membrane.
This opinion, however, is in direct contradiction to that of Lenkart and Newport and many others, who hold that the albumen, which gathers around the yolk in the oviduct, hinders the penetration of the spermatozoa into the yolk. When Albini had collected his facts he came to the conclusion that, in the case of animals which bear many young, the last are mostly male, and explains this by the hypothesis that the ova passing through the Fallopian tube thrust the semen back, so that the ova which come behind are therefore fertilized in a more advanced stage.
Meyer believes that he has incontestably proved against Ahlfeld that the sex is determined at conception. He does not appear to be disposed to admit the existence of male and female ova in the ovary; but he thinks it absolutely certain that the sex is determined at conception by the reciprocal action of the ovum and the semen. This view follows from the fact that, as Thury’s theory demands, a fertilization and a determination of the sex must necessarily take place as regards time either at the beginning or the end of the mingling of semen and ovum.
The longer the ovum exists free from the ovary, the longer it remains without the surrounding of those elements (contained in the ovary) which are necessary to it. Apparently, in consequence of the absence of these elements, it is all the time drawing nearer extinction, or it may at least become gradually less capable of maintaining its own sex—which is feminine. At least, it appears, before it is overtaken by the total extinction which threatens it if it is not fertilized, to lose the energy necessary, when fertilization ensues, to maintain its sex, and so may become fitted to assume the opposite masculine sex. This much, however, seems to be quite certain, according to Mayerhofer, that the human ovary does not contain male and female ova already possessed of sex. Equally impossible is it to imagine male and female seminal filaments (spermatozoa) already existing in the organism, and provided with distinct capacities for generating definite sexes. We are unacquainted with any special anatomical signs indicating any such distinction, and do not, even after microscopic investigation, find ourselves prompted to assume the existence of such distinct forms as would allow us to conclude the existence of so fundamental a difference. It is true that in many of the lower animals different forms of spermatozoa are known. These are developed in one and the same testicle, and under the microscope whisk about confusedly with vivacious movements. We find this in the case of a kind of snail (Murex brandaris). If we observe a drop of the semen of this creature diluted with sea water, the greater number of the spermatozoa, possessing head, central portion, and tail, move about very energetically. Amongst them are other spermatozoa, distinctly larger and of different form, whose shape suggests spindle-like elements, ending in thin thread-like tails. All these objects exhibit a striking vivacity of movement. Whether these objects represent a particular kind of spermatozoa (as some have supposed), exhibiting definite sexual character, or whether they are not cells, striking on account of their movements, out of which spermatozoa are developed (the so-called spermatides or spermatogonia, transition forms out of which spermatozoa are developed), is at present an open question.
H. A. Pagenstecher attempted an important readjustment of Thury’s theory, and tried to show that it might be made concordant with what had been elucidated by previous observations. He holds fast to the axiom (Joh. Muller, Home, Geoffrey St. Hilaire, etc.), that the embryo is at first sexless, and that the ovum after its fertilization still has this character, and must possess the potentiality of developing its sex in two different directions. The factors which determine sex must be external to the embryo.
Pagenstecher remarks that the relations which have existed anterior to the fertilization of the ovum, as well as its age (with which its ripeness is connected), are from the outset without influence on sex.
The embryonal germ, before its fertilization, is an embryo whose sexual development is undetermined. In this case fertilization acts as an external factor in the direction of determining the sexual quality of this indeterminate embryo.
The act of impregnation would be of influence upon the sex of the embryo in accordance with the character of the father. That follows from Pagenstecher’s explanations of Hofacker’s observations. According to Hofacker we get from men of twenty-four years of age and upwards, as also from sheep of a certain age, an average of a greater number of males. In the case of mothers, also, as we have already pointed out, the sexually-stronger age (Lenkart, Girou de Buzareingues, Hofacker, Morel de Vindé, Sadler) and the food have an influence upon the majority of births of female individuals. Here should be added the experience of Nasse and Van den Bosch. The observations of Dzierzon, von Siebold, Lenkart, and von Berlepsh, on the development of sex in bees, and, according to von Siebold, among the Psychids, should also be taken into consideration. When the females of certain Psychids are not impregnated they lay only female ova. If they are impregnated, male ova appear also. The tree-lice (Cestoni, Réaumur) give birth to living young without impregnation. These are at first only female, afterwards males appear as well. After this impregnation commences, and the females begin to lay ova.
The experiments of Knight, who found that melons and cucumbers produce male blossoms under higher temperature and female under lower (which was verified by Mauz), demonstrate that, in this case, such external factors as warmth, light, dryness, have an influence upon sex. Pagenstecher, however, believes that the conditions of origin of sex are not the same in animals and plants. We must not, he says, from these observations draw conclusions off-hand respecting the sexual propagation of plants nor of animals in general.