56 THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



this organization is invisible, it is imbued with an invincibility which, when 

 set in motion at the time of fertilization, drives the developmental processes 

 onward until final fulfillment is achieved in the fully formed body of the 

 adult organism. 



Beyond the fundamental changes effected in the developing egg while in 

 the ovary, the latter structure has still other roles to maintain. Through the 

 mediation of the hormones produced within the confines of the ovarian sub- 

 stance, the female parent is prepared to assume the responsibilities of repro- 

 duction. In addition, in many vertebrates the further responsibility of taking 

 care of the young during the embryonic period stems from the hormones 

 produced in the ovary. In some vertebrates, the instinct of parental care of 

 the young after hatching or after birth indirectly is linked to ovarian-pituitary 

 relationships. Because of these profound and far-reaching influences which 

 the ovary possesses in producing the new individual, it must be regarded as 

 the dynamic center of reproduction for most animal species. 



B. Preformationism, Past and Present 



The above statement relative to the importance of ovarian influences and 

 of the female parent is a position far removed from that held by some in the 

 past. An ancient belief elevated the male parent and his "seed" or semen. 

 As Cole, F. J., '30, p. 38, so aptly places the thinking of certain learned 

 sources during the 16th century: "The uterus is regarded as the 'till'd ground 

 for to sow the seeds on' — a popular idea, based obviously on the analogy 

 with plants, which prevailed long before and after this period. The seed of 

 the male is therefore the chief agent in generation, but cannot produce an 

 embryo without the cooperation of the female, and whether the result is male 

 or female depends on which side of the uterus the seed falls, the time of the 

 year, temperature, and the incidence of menstruation." Or, in reference to 

 the Leeuwenhoek's belief in an intangible preformationism. Cole, F. J., '30, 

 p. 57, states: "He asserts that every spermatic animalcule of the ram contains 

 a lamb, but it does not assume the external appearance of a lamb until it has 

 been nourished and grown in the uterus of the female." This statement of 

 A. van Leeuwenhoek (1632-1723) was made as a criticism of N. Hartsoeker 

 (1656-1725) whose extreme adherence to a seminal preformationism led 

 him to picture the preformed body of the human individual, the homonculus, 

 encased within the head of the spermatozoon (fig. 26). Hartsoeker, however, 

 later abandoned this idea. 



In fairness it should be observed that the egg during these years did not 

 lack champions who extolled its importance. While the Animalculists consid- 

 ered the sperm cell as the vital element in reproduction, the Ovists, such as 

 Swammerdam (1637-80), Haller (1708-77), Bonnet (1720-93) and Spal- 

 lanzani (1729-99) believed that the pre-existing parts of the new individual 

 were contained or preformed within the egg. 



