i66 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



3-7. Marcello Malpighi: Micro- Iconography and Preforma- 

 tionism 



In the year 1672, Marcello Malpighi, who had for many years 

 previously been working on various embryological problems with the 

 aid of the simple microscope, published his tractates De Ovo Incubato 

 and De Formatione Pulli in Ovo. In spite of its great importance, there 

 is not much to be said about it, for it is anything but a voluminous 

 work. The plates in which Malpighi represented the appearances he 

 had seen in his examination of the embryo at different stages are 

 beautiful, and some of them are reproduced. Description of the embryo 

 was now pushed back into the very first hours of incubation, and it 

 is interesting to note that Malpighi could not have done his work 

 without Harvey, whose name he mentions on his first page, and who 

 pointed out the cicatricula as the place where development began, 

 and therefore, as Malpighi must have reasoned, the place where 

 microscopic study would be very profitable. Now for the first time 

 the neural groove was described, the optic vesicles, the somites, and 

 the earliest blood-vessels. 



Malpighi opened the modern phase of the controversy preformation 

 versus epigenesis by supporting the former view. Embryogeny, he 

 held, is not comparable to the building of an artificial machine, in 

 which one part is made after another part, and all the parts gradually 

 "assembled", but takes place rather by an unfolding of what was 

 already there, like a Japanese paper flower in water. He was led 

 to this belief by the fact that development goes on after fertilisation 

 as the tgg passes down the oviduct, and in the most recently laid 

 eggs gastrulation is already over, so that in his researches he could 

 never find an absolutely undivided egg-cell. It is curious to note 

 that he says his experiments were done "mense Augusti, magno vigente 

 calore'\ so that more than a usual degree of development would 

 have taken place overnight. Had he examined the cicatriculae in 

 hens' eggs before laying, he would very probably not have formed 

 this theory, and the epigenesis controversy would have been settled 

 with Harvey. Another influence which was unfavourable to the 

 epigenetic position was that it was Aristotelian, and therefore un- 

 fashionable. Yet Malpighi's view was much more sensible than many 

 which succeeded it, for he did not maintain a perfectly equal swelling 

 up of all parts existing at the start, but rather an unequal unfolding, 



