Ovum / by Allen Thomson.

  • Allen Thomson
Date:
[1856]
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Licence: Public Domain Mark

Credit: Ovum / by Allen Thomson. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    some other animals, in which, had it been present, it could scarcely have escaped so careful a scrutiny, warrant the belief that in a certain number of animals the spermatozoa do actually penetrate the apparently entire egg- covering. It is not my design to enter here upon the consideration of the mode and nature of the action exerted by the spermatic matter or the spermatozoa in producing the changes of fecundation. Upon this subject the reader may with great advantage and interest consult the latter part of the article Semen in this Cyclopsedia by R. Wagner and Leuckart, the papers of the late Mr. Newport in several recent volumes of the Philosophical Trans- actions, and the learned article by Professor Leuckart on Generation contained in the fourth volume of R. Wagner’s Handbuch der Physiologie. I will only remark in passing that from Mr. Newport’s and other researches it appears that while the actual mixture of an appreciable quantity of the spermatic sub- stance is necessary to induce fecundation, the extreme rapidity with which the action takes place, the minuteness of the quantity of the spermatic matter which is sufficient to induce it, and the fact now observed in a variety of instances that the spermatozoa which have entered the ovum remain apparently little changed for a considerable time after the changes of the ovum consequent on fecunda- tion have made some progress,— lead to the conclusion that there is something in the nature of this action inconsistent with the idea that it is one of mere combination in substance of the developed contents of the male and female generative products. But whether this is to be referred to the class of “ contact actions ” of which themselves so little is known, or to what other kind of action it may be compared, the ascertained facts do not enable us in the least to deter- mine. The almost universal presence of vi- bratory motion in the spermatozoa during the time in which they retain their fecundating power, naturally led physiologists to connect that motion with the fecundating action ; but on the other hand, the occasional, though rare examples in which the spermatozoa are en- tirely motionless, seem sufficient to cause the rejection of the view that the force which produces the vibratory motion is identical with that which calls forth the series of histogenetic and organogenetic changes which result from fecundation. But the consideration of this subject would lead us into the discussion of the whole question of vital forces, which in its present unsatisfactory state it is desirable to avoid. The physiologist agrees, for the sake of con- venience of expression, to adopt the terms of power, property, force, &c., to denote the con- ditions necessary for the occurrence of certain actions or changes. He employs the term vital force merely as the indication of the supposed cause or causes of an ascertained regular sequence of vital jphenomena ; but all philosophical accuracy rejects the idea of any unseen separate and single force which is at work in bringing about the sequence in ques- tion. The fecundating power of the semen is an expression used only for convenience to denote the invariable sequence or relation as cause and effect which has been observed to subsist between the contact of spermatic matter with the ovum, and the changes in the latter which follow on the act of fecundation. We might with as much propriety have given a name to a separate power residing in the egg or its germ which render it susceptible of fecundation, as of a special power belonging to the semen by which that susceptibility of the ovum is acted upon. The efficient cause of the process of fecundation can only' be educed, as in all physical as well as vital changes, from a perfect knowledge of all its phenomena, and the statement of the efficient cause of such actions is only the expression of the most general and best known law to which a full acquaintance with the phenomena enables them to be reduced. Fecundation is to be regarded as a purely vital change, seeing that it takes place only in the usual conditions of vitality; but, like all other vital changes, it appears more probable that a variety of conditions of the organic matter rather than any one known property or condition are necessary for its occurrence. In endeavouring to deduce the most ge- neral phenomena which accompany this re - markable change, it may be said that fe- cundation consists essentially in the mutual action of two different organised bodies, which are respectively formed from two different cells ; the ovigerm and the sperm- germ. If we may form any general con- clusion from what may be so well observed in Nematoid Worms, the development of the ovum and the .spermatic cells from their re- spective germs is remarkably similar, for in both the internal cell is developed from a minute molecule from within, while the ex- ternal part is deposited from without. The spermatozoa are formed in connection with the nucleus or nuclei of the sperm-cell; and the germinal part of the ovum, though it con- sists mainly of the granular part of the yolk, which is directly formative, very probably comprehends also in some shape or other the effused contents of the germinal vesicle. In this way, then, we may conjecture that in the act of fecundation the products of the original cell-germs meet and combine or mutually influence each other. The cell-germs, then, are the links in the chain of organic connec- tion between either or both the parents and the progeny capable of being developed from the fecundated ovum. Such a view, though still in a great measure speculative, seems to be in accordance with the facts known as to the perfect transmission of the structure and qualities of either or of both parents to the offspring.' 6. Immediate effects of fecundation on the ovum ; segmentation, and first changes ot the ovum related to the commencement of em- bryonic development. It does not come within the scope of the present article to describe in detail the pro-