854 GENERATION. 



The study of human generation will naturally assume the following course: First, 

 the female organs of generation and the formation of the female element, the ovum ; 

 second the discharge of the ovum and the phenomena which attend this process ; third, 

 the male organs and the development and discharge of the male elements, the spermato- 

 zoids; fourth, the union of the two elements of generation, or fecundation; fifth, the 

 development of the fecundated ovum into the fetus at term ; sixth, the development 

 of the body after birth and at different ages, or stages of existence ; finally, the natural 

 cessation of the so-called vital functions, or physiological death. 



Sexual Generation. 



Before we describe the actual phenomena of sexual generation, as they are observed 

 in man and the mammalia, it will be interesting to note some of the salient points in the 

 history of our knowledge of this process in the inferior animals. This we can do, with- 

 out exceeding the limits we have laid down in our general remarks. 



In the history of sexual generation, there seems to have been a limiting line between 

 the production of animals from preexisting organisms and of those produced in some 

 unknown manner, or, as it has been said, spontaneously. This line of distinction has 

 always receded toward organisms lower and lower in the scale of being, with our advance 

 in positive knowledge. The ancients understood that the higher animals required for 

 their production a concourse of the sexes; but they thought that many fishes, reptiles, 

 insects, worms, etc., were produced spontaneously. Indeed, with the limited knowledge 

 of natural history possessed by Aristotle and those who succeeded him for many hun- 

 dred years, the classes of animals said to be produced spontaneously represented simply 

 those, the generation of which was not understood. But, as the habits of many animals 

 became better understood, more and more of them were observed to lay eggs, which 

 were found to undergo development. 



Dating from Aristotle, who lived between three and four hundred years B. c., it was 

 nearly two thousand years before any thing was known of the generation of insects ; 

 the difficulty here being that the young are first in a larval state and bear no resem- 

 blance to the parents. Anterior to the experiments of Eedi, it was thought that certain 

 organic matters in course of putrefaction developed living organisms, as maggots in meat 

 and the larvae in cheese. 



We refer to the experiments of Redi, made about the year 1668, for the reason that 



these mark an era in our knowledge of the process of generation. This observer, noting 



that flies frequently lighted upon meat when it was exposed, simply protected it by 



gauze and found that no maggots were developed, while other pieces of meat, placed 



under the same conditions, except that the flies had free access to them, developed mag- 



\ m great numbers. By this simple experiment, Redi showed that the maggots in 



putrefying meat were produced by insects and not by the meat ; but it remained for 



Swammerdam and Vallisneri to study the metamorphoses of insects, and to show how 



he eggs were developed, first into sexless larvae, and finally into perfect beings resembling 



le parents. It is curious to note the condition of science anterior to Redi and Vallis- 



and compare it with the ideas that are current at the present day. When -maggots 



red in putrefying meat, they were thought to be produced by a spontaneous aggre- 



orgamc particles, simply because observers knew of no other way in which 



?s could come into existence. Now, the advocates of spontaneous generation 



same ideas as those advanced anterior to 1668 ; but, in the place of meat, they 



infusions, and for maggots, they substitute infusorial animalcules. It is 



that the discussion of the question then was as energetic as it is now ; but the 



of uoh d anC - 6S m a , kn wled ^ of the generation of insects has swept away the memorv 



.scions, if they existed, as future advances may possibly cause many of the 



controversial writings of the present day to pass into oblivion 



