Problems, Concepts and Their History 



egg studied after exposvire to the heat of the 

 August sun in Bologna is "unincubated" 

 only with reference to the hen — but the 

 work was no less influential than had it 

 been founded on a different premise. Mal- 

 pighi's primary contribution was his success- 

 ful presentation for the first time of visible 

 evidence on the detailed constitution of the 

 young embryo. And evidence adduced by 

 one of the new tools was as certain in the 

 seventeenth as in the twentieth century to 

 draw popular enthusiasm. 



It was a function of his times that such 

 evidence could be construed as support for 

 embryological theory. What Malpighi saw 

 and figured could be interpreted according 

 to postvdates compatible with Descartes' 

 hypothesis of the infinite divisibility of 

 matter; what he figured could be general- 

 ized into theories implying the embryo to 

 be the same kind of "earthly machine" as 

 Descartes' adult, and the concepts which 

 were to incorporate his observations into the 

 doctrine of preformation were crystallizing 

 in many minds. Malpighi was no lone 

 prophet of the new embryology. His con- 

 temporaries were going far to cry physical 

 facts to fit a philosophical pattern. Croone, 

 at much the same time, was making some- 

 what similar claims for the pre-existence of 

 the chick in the egg, on the basis of a fan- 

 tastically egregious error, mistaking a frag- 

 ment of vitelline membrane for the embryo 

 (Cole, '44). Swammerdam had in 1672 ex- 

 pressed a somewhat comparable concept for 

 the egg of the frog, and Grew an analogous 

 one for plants the same year. Malebranche, 

 on the basis of observations as well as specu- 

 lation, was expressing similar conclusions 

 and generalizing the doctrine for plants and 

 animals on a strong philosophical founda- 

 tion (Schrecker, '38). For Leibniz, preforma- 

 tion was not only a metaphysical but also a 

 strictly biological postulate which he related 

 to his concept of the fixity of species. Bonnet, 

 after his discovery of parthenogenesis in 

 aphids, made preformation the basis for all 

 his biological and philosophical specula- 

 tions; the theory was supported by all the 

 weighty authority of Haller, and even by 

 such advanced experimentalists as Spallan- 

 zani and Reaumvir. 



Vallisnieri's specvilations on the possibility 

 that not only the whole human race but also 

 all human parasites were represented in the 

 ovaries of Eve, and Hartsoeker's calcvilation 

 of the necessary size of a rabbit large enough 

 to enclose all rabbits from the beginning of 

 time; Dalenpatius' absurd claims to have 



seen the homunculus in the spermatozoon, 

 and all the foolish arguments between ovists 

 and aniraalculists exemplified the extremes 

 to which the doctrine was led; and such 

 ridiculous claims served primarily to over- 

 burden it until it was close to collapse under 

 its own weight. But it also fell, as it rose, on 

 the basis of more serious philosophical prin- 

 ciples; again a philosophical need had cre- 

 ated a demand which again an observational 

 embryologist — this time Caspar Friedrich 

 Wolff— was to fulfill. 



Wolff started out with a full apprecia- 

 tion of the philosophical limitations to em- 

 bryological progress implied by the pre- 

 formation doctrine: "Qui igitur systemata 

 praedelineationis tradunt, generationem non 

 explicant, sed, earn non dari, affirmant" 

 (1759; cited from 1774 edition, p. xii); those 

 who adopt the systems of predelineation do 

 not explain generation but affirm that it 

 does not occur. He was to launch his own 

 attack from two sides, from the philosopher's 

 and the observer's, but he started from the 

 former's position: "Verum explicat genera- 

 tionem, qui ex traditis principiis & legibus 

 partes corporis & modum compositionis de- 

 ducit. . . . Et absoluit theoriam generationis, 

 qui totum corpus generatum ex principiis & 

 legibus illis eo modo deducit" (ibid., pp. xii, 

 xiii). 



Deducing the body from principles and 

 laws is the philosopher's way, not the em- 

 bryologist's; but Wolff's virtue was that he 

 felt compelled to supplement his abstruse 

 reasoning by examination of his material 

 and he was thus able to svibstantiate his 

 theory. Aristotle, as a Greek, had experi- 

 enced no such compulsion; Harvey had had 

 the will but not the way; Wolff had not 

 only the desire, but also the good fortune 

 and the good skill to be both philosophically 

 and observationally accvirate within closer 

 limits than his predecessors, and posterity 

 concurs in von Baer's evaluation of some of 

 his work as at that time "die grosste Meis- 

 terarbeit, die wir aus dem Felde der be- 

 obachtenden Naturwissenschaften kennen" 

 (1837, II, 12). 



Starting from highly abstract speculations 

 concerning growth and nourishment in theii 

 relation to what we should call differentia- 

 tion, he took up in particular detail (to be 

 sure, some years before Goethe, but also, 

 well over a millennium later than Theophras- 

 tus) the metamorphosis of plants, pointing 

 out that the rudiments of leaves are basically 

 similar to those of the parts of the flower and 

 that the rudiments of both alike are derived 



