366 PROGRESS OF SCIENCE IN THE CENTURY. 



glasses (perspecillce) Harvey demonstrated the 

 connection between the " cicatricula " of the yolk 

 and the rudiments of the chick, and he also observed 

 some of the stages of uterine gestation in mammals. 

 He maintained (1) that every animal is produced 

 from an ovum (ovum esse primordium commune 

 omnibus animalibus), and (2) that the organs arise 

 by new formation (epigenesis) and not from the 

 mere expansion of some invisible preformation, or, 

 in other words, that in the primordium " no part of 

 future organism exists de facto, but all parts inhere 

 in potentia." But it has to be carefully remembered 

 that he had no way of accounting for the primordium 

 with which he started ; he admitted that it might pro- 

 ceed from parents, or might arise spontaneously, or 

 out of putrefaction. It was not he who coined the 

 aphorism " omne vivum ex ovo" for which he often 

 gets credit. Even if he had said it, the statement 

 would not have meant to him what it means to us. 



Early Observations. Malpighi (1672), using a 

 microscope with remarkable skill, traced back the 

 chick-embryo into the recesses of the cicatricula 

 lying on the top of the yolk, but he missed a magnifi- 

 cent discovery by supposing that the rudiments of 

 the organs pre-existed in the egg. Spermatozoa were, 

 it is generally believed, discovered by Leeuwenhoek's 

 pupil, Ludwig Hamm, in 1677, though Hartsoeker 

 afterwards claimed priority by three years : a ques- 

 tion of little interest, since neither understood what 

 he saw. In 1664, Steno had given the ovary its 

 present designation, and De Graaf had interpreted 

 the vesicles of this organ (" the Graafian follicles ") 

 as for the most part equivalent to the ova which he 

 thought he had discovered in the oviduct. 



Theory of Preformation. In spite of the begin- 



