THE ULTIMATE SEX-ELEMENTS. 81 



A side controversy of the time arose between two schools, who 

 called each other ' ' ovists ' ' and ' ' animalculists. ' ' The former main- 

 tained that the female germ -element was the more important, and 

 only required to be as it were awakened by the male element to begin 

 the process of unfolding. The animalculists, on the other hand, 

 asserted the claims of the sperm to be the bearer of the miniature nest 

 of organism within organism, and supposed that it only required to be 

 fed by the ovum to enlarge and unfold the first of the models which 

 it concealed. 



id) Wolff's Reassertio?i of Epigenesis. — The above ingenious 

 construction was rudely shaken down, however, in 1759, when 

 Caspar Friedrich Wolff showed, in his doctorial dissertation, the 

 illegitimacy of the suppositions which lay at the root of the preforma- 

 tion theory. He traced the chick back to a layer of organized par- 

 ticles (the familiar cells of today), in which there was no likeness of 

 the future embryo, far less adult. More than that, he followed the 

 disposition of these primitive elements to the upbuilding of some of 

 the important organs. He undoubtedly reached too far in his 

 emphasis on the entire simplicity of the germ, and many of his details 

 were mistaken; but none the less did he recall embryologists from 

 speculation to take the facts as they found them, and lay the founda- 

 tion of modern embryology in the fact that organization was gradu- 

 ally acquired by an observable process of development. 



(e) Wolff's Successors. — The important conclusion reached bv 

 Wolff remained for about sixty years without effect. In 1817, 

 Christian Pander took up embryological research exactly where W r olff 

 had left it, and worked out the history of the chick in more exact 

 detail. In 1824, Prevost and Dumas noticed the division of the ovum 

 into masses; and in the following year Purkinje discovered the nucleus 

 or "germinal vesicle." Von Baer followed up his friend Pander's 

 work, and in 1827 made the memorable discovery of the mammalian 

 ovum, which he traced from uterus to oviduct, and then to its position 

 in the ovary itself. Thus, after a century and a half, De Graaf's 

 endeavor was at length fulfilled. Soon afterwards, Wagner, von 

 Siebold, and others, elucidated what was still hidden from von Baer — 

 the real nature of the spermatozoa. Meanwhile, Bichat's analysis 

 ri8oi) of the organism into tissues, was with improved appliances 

 deepened in the casual description of " cells" ; and an important gen- 

 eralization had its forecast in 1835, when Johannes Miiller pointed out 

 in the vertebrate notochord the existence of cells resembline those 

 of plants. 



III. The Cell-theory. — Without continuing the history further, 

 we must simply note that in 1838 Schleiden . referred all vegetable 



