426 



GENERATION. 



Jlefore treating in detail of Human Gene- 

 ration, we introduce some remarks on the 

 nature of the reproductive function in genera], 

 and a sketch of the principal varieties of the 

 forms it assumes in different classes of ani- 

 mals. 



I. THE FUNCTION OF REPRODUCTION GENE- 

 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 peculiai 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. 

 Hence, 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 ijune- 

 rative processes. For, if we except the re- 

 markable investigations of Aristotle, Fabricius, 

 Harvey, Malpighi, Wolff, and lialler, 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. 



At the same time it may be allowed that the 

 fact that the mere contact of the male seminal 

 fluid seems to awaken and call forth from tlie 

 otherwise inanimate egg all those vital powers 

 which are afterwards concerned in sustaining 

 the life of the new being, is one of the most 

 striking and simple examples of vital agency, 

 and one less suited than most others to be 

 observed or experimentally investigated. The 

 theoretical physiologist, in contemplating this 

 fact, is apt to conceive that here he lias ar- 

 rived at one of the primitive causes or foun- 

 dations of animal life, and that he has here 

 obtained the key to many of its hidden won- 



