DEVELOPMENT OF THE INDIVIDUAL 



561 



offspring. Furthermore, this was during the 

 time when the male sex was considered all 

 important, the female being passive in her 

 social life as well as her biological life. The 

 appearance of female characteristics in the 

 offspring was apparently ignored. More- 

 over, the finding of the placenta attached to 

 the embryo by the umbilical cord furthered 

 the concept that the female functioned only 

 in nourishing; the fetus. The idea that both 

 sexes contributed to the offspring appar- 

 ently came much later. 



With the actual discovery of the human 

 sperm by Ludwig Hamm, who first saw it 

 through a crude microscope in about 1677 

 and brought it to the attention of Leeuwen- 

 hoek, the importance of the male retained 

 its place. This was further emphasized by 

 the work of Hartsoeker, who not only 

 claimed to have seen the human sperm first 

 but who also went so far as to draw a minia- 

 ture fetus within the head of the sperma- 

 tozoan and thus advanced the idea of the 

 homunculus (Fig. 23-1). This led to the 

 establishment of the preformation school 

 which included those who believed that the 

 human embryo was completely fonned 

 within the sperm and had merely to unfold 

 during its development. Impetus was given 

 to this idea by Malpighi (1672), who con- 

 cluded that the chick was fully formed, 

 though in miniature, at the time the egg 

 was laid. This was probably due to an er- 

 ror that could easily arise from a study of 

 an egg that remained several hours ( 10-15) 

 within the oviduct where development of 

 the chick could proceed. However, because 

 of the obvious existence of large eggs, such 

 as those of birds and reptiles, there devel- 

 oped a school which believed that the egg 

 was the center of development. This meant 

 there were two schools of thought among 

 performationists, the spermists and the 

 ovists. 



An interesting aspect of this controversy 

 was the development of the encasement 

 theory. One group of followers believed 

 that the child was derived completely from 



the egg and that the egg contained a minute 

 human being within it. If the egg in ques- 

 tion contained a diminutive woman, within 

 the eggs of her ovary were still more minute 

 women and so on, each encased in the pre- 

 ceding. From tliis point of view the first 

 woman contained all of the future genera- 

 tions wrapped one within the other. The 

 absurdity of this theory became apparent 



Fig. 23-1. One of the early schools of embryology was 

 that of the spermists, who bei.eved that \he child was 

 preformed in the sperm and merely unfolded within 

 the confines of the female uterus. Among followers of 

 this concept was Hartsoeker, who published a drawing 

 in 1678 similar to the one shown here and advanced 

 the idea of the homunculus. The human sperm as it 

 appears under a modern microscope is shown for 

 comparison. 



with the discovery of the human egg by 

 Von Baer in 1827 and by those who took the 

 time to make a few mathematical calcula-r 

 tions on the size that Eve must have been 

 to house all future senerations. All of these 

 theories seem strange to us now, but when 

 they were advanced they performed a nec- 

 essary function in that they stimulated in- 

 vestigators to search more intensively for 

 an answer which was to come only when 

 instruments became sufficiently perfected 

 to make accurate observations possible. 



THE PATH OF DEVELOPMENT 



By comparing the embryos of any species 

 of animal at varying stages in their develop- 



