Maternal Organs of Reproduction in Animals. 255 



is employed to designate that condition of the female which shows 

 her fitness and desire for the male. Its early or late appearance 

 is governed bj a variety of external circumstances. It is asso- 

 ciated with puberty, and passes off on the approach of old age. In 

 some of our improved breeds of cattle, especially when well kept 

 and tended, oestrum comes on very early in life, and in such in- 

 stances the animal often conceives when she is little more than a 

 year old. These early conceptions, however, too frequently prove 

 injurious, by interfering with the development of the frame of the 

 female, and also by deteriorating the quality of her offspring. Do- 

 mestication, with its ordinary accompaniments, exerts a consider- 

 able stimulating influence on the generative system ; thus some 

 animals which in a state of nature produce but one litter a year, 

 will, when domesticated, bring forth several : such are the dog 

 and pig, The immediate cause of oestrum is the existence of 

 fully matured ova within the ovaries of the female ; and when 

 these escape, without coition and consequent impregnation, we 

 observe a temporary cessation of the desire until other ova are 

 equally perfected. It follows, therefore, that impregnation can 

 only be effected when the ova are in this condition. The time 

 occupied in the development of the ova differs in different animals, 

 hence the variation we witness in their return to the male. The 

 ordinary symptoms of oestrum in the cow and other animals are 

 too well known to render it necessary to repeat them ; and it is 

 sufficient to state that they denote a highly excited state of the 

 system. Impregnation is produced by the fecundating fluid of 

 the male acting on the matured ovum of the female, which action 

 probably takes place in the ovarium. Physiologists are acquainted 

 with many phenomena which illustrate this. The way in which 

 the male or seminal fluid finds its course through the body and 

 horns of the uterus, and thence through the Fallopian tube to the 

 ovarium, is disputed. Its conveyance, however, is generally be- 

 lieved to be effected through the agency of moving filaments, called 

 spermatozoa, with which it abounds. Hence it is all important 

 that the Fallopian tubes should be pervious, or impregnation can- 

 not take place. If their passage be obliterated, as w T e have often 

 proved by the experiment of passing a ligature around them, the 

 animal is as effectually rendered non-productive as if the whole 

 parts had been taken away. The above facts explain how it is that, 

 in the ordinary operation of spaying, the simple removal of the 

 ovaries, leaving in situ the uterus with its horns and Fallopian 

 tubes, destroys the desire as well as the power of conception, and 

 when by accident or otherwise the operator leaves behind an 

 ovarium, all other parts being cut away, the animal returns to the 

 male, notwithstanding she is sterile. 



The impregnated ovum when it bursts and escapes from its 



