692 OF REPRODUCTION. 



continual direction of the mind towards objects which awaken the sexual pro- 

 pensity ( 626, note) ; and thus, if intercourse be very frequent, a much larger 

 quantity will altogether be produced, although the amount emitted at each 

 period will be less. The formation of the secretion seems of itself to be a 

 much greater tax upon the corporeal powers, than might have been supposed 

 a priori: and it is a well-known fact, that the highest degree of bodily vigour 

 is inconsistent with more than a very moderate indulgence in sexual inter- 

 course ; whilst nothing is more certain to reduce the powers, both of body 

 and mind, than excess in this respect. These principles, which are of great 

 importance in the regulation of the health, are but results of the general law, 

 which prevails equally in the Vegetable and Animal kingdoms, that the 

 Development of the Individual, and the Reproduction of the Species, stand 

 in an inverse ratio to each other. 



3. Jlction of the Female. 



905. The essential part of the Female Generative system is that in which 

 the Ova are prepared ; the other organs are merely accessory, and 'are not to 

 be found in a large proportion of the Animal kingdom. In many of the lower 

 animals, the Ovaria and Testes are so extremely like each other, that the dif- 

 ference between them can scarcely be distinguished ; and the same has already 

 been stated, regarding the condition of these organs in Man, at an early period 

 of development ( 866 6). The fact is one of no small interest. In the lower 

 animals, the Ovarium consists of a loose tissue containing many cells, in which 

 the Ova are formed, and from which they escape by the rupture of the cell- 

 walls ; in the higher animals, as in the Human female, the tissue of the Ova- 

 rium is more compact, forming what is known as the stroma; and the Ova, 

 except when they are approaching maturity, can only be distinguished in the 

 interstices of this, by the aid of a high magnifying power. We owe to Dr. 

 Barry the discovery of the earliest stages in the production of the Ovum and 

 its accessory parts, in Mammalia and other Vertebrata. In order to under- 

 stand his account, however, it will be necessary that the parts of which the 

 ovum consists should be previously understood. Taking the Fowl's Egg as a 

 familiar illustration, it must be remarked, in the first place, that neither the 

 albumen which forms the white, nor the shell-membrane with its testaceous 

 covering, exist in the Ovarian Ovum ; these portions being added during its 

 passage along the oviduct. The parts which we have to analyze, are the 

 Yolk-membrane and its contents. Within the Yolk-membrane, we find in the 

 first place, the Yolk itself; a substance consisting in part of albuminous gran- 

 ules, and in part of oily globules. Towards the centre, the character of the 

 Yolk in some degree changes ; its colour being lighter, and the granules pre- 

 senting more the appearance of cells, with minuter globules in their interior. 

 The central portion is termed the discus vitellinus. Occupying the centre of 

 the yolk (in the immature ovulum) is a large cell, very distinct in aspect from 

 the rest, and having a well-marked nucleus upon its walls. This is termed 

 the germinal vesicle; and the nucleus, the germinal spot. The Mammalian 

 Ovum contains exactly the same parts; but the yolk is much smaller in pro- 

 portion, and corresponds in character rather with the discus vitellinus, than 

 with the whole yolk of the Bird's egg. The Ovum in all Vertebrated animals 

 is produced within a capsule or bag, the exterior of which is in contact with 

 the stroma of the ovarium ; this has been termed in Mammalia, the Graafian 

 follicle, after the name of its first discoverer ; but the more general and ap- 

 propriate designation of Ovisac has been given to it by Dr. Barry, who has 

 shown that it exists in other classes of Vertebrata. Between the Ovum and 

 the Ovisac, in Oviparous animals, there is scarcely any interval ; but in the 



