I. THE FUNCTION OF REPRODUCTION RALLY CONSIDERED.
1. Introductory remarks.—The process by which the young of animals are formed has; from the earliest periods of science, always been an object of peculiar interest and atten tion to inquirers into the functions of animated beings. Scientific men as well as the more ignorant have looked with a mixed feeling of wonder and admiration upon the intricate changes which precede and accompany the first appearance and gradual formation of all the different textures and organs belonging to animal bodies. The gradual construction or building up of the whole frame-work of the animal body, and its various important organs, —the formation of the nerves and brain that feel and think, the muscles that move, the blood with its containing organs that propel it and apply it to the purposes of nutrition,— the appearance step by step of all the remark able structures out of which the different organs are formed,—the development of the appropriate vital powers of each of them,— the comparatively simple structure of the sub stance of the egg, and the impossibility of detecting in it by the most exact scrutiny, before the commencement of the formative process, any appearance of the parts after wards arising there—have naturally led phy siologists to inquire minutely into the pro perties of that egg, and the process by which so remarkable a production is generated. The ascertained fact that the egg possesses vital powers belonging to itself, and that its life is in a great measure independent of that of its parents,—that the vital powers of the egg are capable of being called into operation and in fluenced in many animals by determinate external physical agents, such as heat, air, light, and electricity,—the obscure nature of the influence exerted by the male upon the female product in the perfecting of the egg,— the preservation of the specific distinctions of animals from one generation to another in un deviating succession,—the transmission of oc casional varieties or peculiarities of form and of hereditary resemblances from parent to offspring,—and, in fine, the important relation which the generative process bears to other functions of the animal economy, are among the more prominent circumstances which, while they throw a certain air of mystery over the functions of reproduction, have at the same time given them an interest in the eyes of the physiologist, which increases as his acquaint ance with their details becomes more ex tended.
It is a common remark that generation is at once the most obscure and the most wonderful of the processes occurring in organized bodies.
IIence,perhaps, it has happened that,while there are few subjects of physiological inquiry upon which so many authors have written, there is none upon which so many have freely indulged their fancies in framing unwarranted hypotheses and absurd speculations. This is an error which belongs to the early stage of investigation in most branches of natural knowledge, and which in the instance before us may be traced very directly to the comparative want of cor rect information which for a long time pre vailed regarding the phenomena of the gene rative processes. For, if we except the re markable investigations of Aristotle, Fabricius, Ilarvey, Malpighi, Wolff, and Haller, it may be said that it is only towards the conclusion of the last or the commencement of the pre sent century that our subject has been studied with that accuracy of observation and freedom from hypothesis which are calcu lated to insure steady progress in the attain ment of physical knowledge. When ex tended observation shall have rendered more familiar to the physiologist the different steps of the intricate processes by which an egg is formed and the young animal is developed from it, although he may not cease to admire the changes in which these processes consist, the feeling of wonder will be in a great mea sure lost to him ; and he will not be inclined to look upon the gradual formation and growth of the child as more extraordinary than the constant and regular nutrition of the fully formed body. Are the inscrutable workings of the brain and nerves, the constant energy of the beating heart, the unwearied and pow erful exertions of the voluntary muscles, the secretion of different fluids from the glands, and the regular supply of suitable organic materials to all parts of the body, so as to maintain the healthy structure of each and fit them for the performance of their respective offices, less remarkable and astonishing, or, in other words, less far removed from our accurate knowledge and comprehension, than the first origin and early growth of the same organs at a time when both their structure and functions are greatly more simple ? Certainly not. These remarkable changes are all objects of wonder to the vulgar in proportion as they are unknown. The man of science regards the ultimate cause of all vital processes as equally inexplicable, and, aware of the bounds set to his knowledge of life, limits his inquiries con cerning its various processes to the investigation of their phenomena.