GENERATION. 



427 



ders : lie passes the limits which ought to 

 bound his inquiries, and in most instances 

 invents fanciful and curious speculations rather 

 than makes sound generalizations of ascer- 

 tained facts. 



2. Theories of generation. The vast num- 

 ber of the theories of generation renders it 

 impossible to mention even the more im- 

 portant in this place. Drelincourt, an author 

 of the last century, brought together so many 

 as two hundred and sixty-two " groundless 

 hypotheses" concerning generation from the 

 writings of his predecessors, " and nothing is 

 more certain," quaintly remarks Blumenbach, 

 " than that Drelincourt's own theory formed 

 the two hundred and sixty-third."* 



Of these theories two principal classes may 

 be distinguished, according as they more di- 

 rectly relate, 1st, to the action of the parent 

 organs, or 2d, to the changes in the egg 

 belonging to the formation of the new animal. 

 Of the first of these classes of theories Haller 

 made three divisions, according as the offspring 

 is supposed to proceed, 1st, exclusively from 

 the organs of the male parent, 2d, entirely from 

 those of the female, or 3d, from the union of 

 the male and female products. The second 

 class of these theories, that, viz. which relates 

 more particularly to the formation of the new 

 animal, may be arranged under two heads, 

 according: as the new animal is supposed, 1st, 

 to be newly formed from amorphous materials 

 at the time when it makes its appearance in 

 the egg, or 2d, to have its parts rendered 

 visible, by their being expanded, unfolded, or 

 evolved from a previously existing though in- 

 visible condition in the germ. 



The greater number of the older theories of 

 generation may then be brought under one or 

 other of the above-mentioned divisions, viz. 

 the theory of the Ovists, of the Spermatists, 

 that of Combination, Evolution or Epigenesis. 



According to the first-mentioned of these 

 hypotheses, or that of the Ovists, the female 

 parent is held to afford all the materials neces- 

 sary for the formation of the offspring, the 

 male doing no more than awakening the forma- 

 tive powers possessed by, and lying dormant 

 in, the female product. This was the theory 

 of Pythagoras, adopted in a modified form by 

 Aristotle ; and we shall afterwards see that it 

 resembles most closely the prevailing opinion 

 of more modern times. The terms, however, 

 in which some of the older authors expressed 

 this theory are very vague, as, for example, in 

 the notion that the embryo or new product 

 " is formed from the menstrual blood of the 

 female, assisted by a sort of moisture descend- 

 ing from the brain during sexual union." 



According to the second theory, or that of 

 the Spermatists, among the early supporters of 

 which Galen may be reckoned, it was supposed 

 that the male semen alone furnished all the 

 vital parts of the new animal, the female 

 organs merely affording the offspring a fit place 

 and suitable materials for its nourishment. 



* See Blumenbach iiber den Bildungstrieb,12mo. 

 Getting. 1791. Anglice by A. Crichton : An Essay 

 on Generation, 12mo. Lond. 1792. 



Immediately upon the discovery of the Sminal 

 animalcules, these minute moving particles 

 were regarded by some as the rudiments of the 

 new animal. They were said to be miniature 

 representations of men, and were styled ho- 

 munculi, one author going so far as to delineate 

 in the seminal animalcule the body, limbs, 

 features, and all the parts of the grown human 

 body. The microscopic animalcules were held 

 by others to be of different sexes, to copulate, 

 and thus to engender male and female off- 

 spring; and the celebrated Leeuwenhoek, who 

 was among the first to observe these animal- 

 cules, described minutely the manner in which 

 they gained the interior of the egg, and held 

 that after their entrance they were retained 

 there by a valvular apparatus. 



The theory of Syngenesis or Combination 

 seems to have been applied principally to the 

 explanation of reproduction of quadrupeds and 

 man, the existence and nature of the ova of which 

 were involved in doubt. This hypothesis con- 

 sists in the supposition that male and female 

 parents both furnish simultaneously some semen 

 or product ; that these products, after sexual 

 union, combine with one another in the uterus, 

 and thus give rise to the egg or structure from 

 which the foetus is formed. In connexion with 

 this theory we may also mention that of Meta- 

 morphosis, according to which a formative 

 substance is held to exist, but is allowed to 

 change its form in order to be converted into 

 the new being ; as also the notion of Buffon 

 that organic molecules universally pervade 

 plants and animals, that these are all endowed 

 with productive powers, that a certain number 

 are employed in the construction of the textures 

 of organized bodies, and that in the process of 

 generation the superabundant quantity of them 

 proceeds to the sexual organs and there consti- 

 tutes the rudiments of the offspring. 



The theories of generation proposed before 

 the commencement of the seventeenth century 

 are either unsatisfactory or erroneous from the 

 entire want of accurate knowledge prevailing 

 before that time regarding the relation of the 

 egg to reproduction. The conversion of one 

 animal into another, constituting equivocal or 

 spontaneous generations, was very generally 

 believed in ; and the process of the formation 

 of the egg was equally ill understood in the 

 lowor and higher classes of animals. It was in 

 the course of the seventeenth century that the 

 labours, first of Harvey, and afterwards of 

 Swammerdam, Redi, Malpighi, De Graaf, and 

 Vallisneri, gave rise to greater precision of 

 knowledge and opinions regarding this subject, 

 and finally established the Harveyan dictum, 

 " omne vivum ex ovo," which may be regarded 

 as the starting - point or basis of modern 

 researches. 



The theories of generation seem after the 

 period of Harvey to have changed somewhat 

 their object, and to have been directed more 

 exclusively to the explanation of the formative 

 process, or the manner in which the parts of 

 the foetus are first formed in the egg and after- 

 wards attain their ultimate structure and con- 

 figuration. 



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