ADDRESS. Ixxvii 



It is of great importance to apprehend Redi's position rightly; for 

 the lines of thought he laid down for lis are those upon which naturalists 

 have heen working ever since. Clearly, he held Biogenesis as against Abio- 

 genesis ; and I shall immediately proceed, in the first place, to inquu-o how 

 far subsequent investigation has borne him out in so doing. 



But Eedi also thought that there were two modes of Biogenesis. By the 

 one method, which is that of common and ordinary occurrence, the living 

 parent gives rise to offspring which passes through the same cycle of changes 

 as itself — like gives rise to like ; and this has been termed Homogeyiesis. 

 By the other mode, the living parent was supposed to give rise to offspring 

 which passed through a totally different series of states from those exhibited 

 by the parent, and did not return into the cycle of the parent : this is what 

 ought to be called Heterogenesis, the offspring being altogether, and perma- 

 nently, unlike the parent. The term Heterogenesis, however, has unfor- 

 tunately been used in a different sense, and M. Milne-Edwards has there- 

 fore substituted for it Xenogenesis, which means the generation of something 

 foreign. After discussing Eedi's hypothesis of universal Biogenesis, then, 

 I shall go on to ask how far the growth of science justifies his other hypo- 

 thesis of Xenogenesis. 



The progress of the hypothesis of Biogenesis was triumphant and un- 

 checked for nearly a century. The application of the microscoi^e to anatomy 

 in the hands of Grew, Leeuwcnhoek, Swammerdam, Lyonet, Yallisnieri, 

 Eeaumur, and other illustrious investigators of nature of that day, displayed 

 such a complexity of organization in the lowest and minutest forms, and 

 everywhere revealed such a prodigality of provision for their multiplication 

 by germs of one sort or another, that the hypothesis of Abiogenesis began 

 to appear not only untrue, but absurd ; and in the middle of the eighteenth 

 century, w'hen Needham and Buffon took up the question, it was almost 

 universally discredited*. 



farete riflepsione a quelle tante sorte cli galle, tli gallozzole, di coccole, di ricci, di calici, di 

 conietU di hipjjole, clie son produtte dalle querce, dalle farnie, da' cerri, da' sugberi, da' 

 lecci e da altri simili alberi da ghianda ; impercioccbe in quelle gallozzole, o particolar- 

 mentc nolle piii grosse, clie si cbiamano coronati, ne' ricci capelluti. clie ciuffoli da' nostri 

 conladini fon dctti; nei ricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzze 

 dclla foglia del leccio si vede evidentissimamente, clie la prima e principale intcnzione 

 della nalura e formare dentro di quelle un animale volante ; vedendosi nel centre della 

 gallozzola un novo, che col crescere e col maturarsi di essa gallozzola va crescendo e matu- 

 rando anch' egli, e cresce altresi a sue tempo quel verme, che nell' novo si racchiude ; il qual 

 verme, quando la gallozzola e finita di niaturare e clie e venuto il terniine destinato al 



8uo nascimento, diventa, di verme che era, una mosca lo vi confesso ingenua- 



mente, che prima d'aver fatte queste mie esperienze intorno alia generazione degl' insetti 

 mi dava a credere, o per dir meglio sospettava, che forse la gallozzola nascesse, perche 

 arrivando la mosca ncl tempo della primavera, e facendo una piccolissima fessura ne' rami 

 pill teneri della quercia, in quella fessura nascondesse uno de suoi semi, il quale fosgo 

 cagione che sbocciasse fuora la gallozzola ; e che mai non si vedessero galle o gallozzole o 

 ricci o cometti o calici o coccole, se non in que' rami, ne' quali le moscbe avessero depositato 

 le loro semenze ; e mi dava ad intendere, che le gallozzole fossero una malattia cagionata 

 nelle querce dalle punture delle mosche, in quella giiisa stessa che dalle punture d' altri 

 animaletti simiglievoli veggiamo crescere de' tumori ne' corpi degli animali." 



* Needham, wi-iting in 1750, says : — ■ 



" Les naturalistes modemcs s'accordent unanimcment a etablir, crmimc une T^rit^ cer- 

 taine, que toute plante vient de sa semence specifique, tout animal d'un couf ou de queJ- 

 que chose d'analogue preexistant dans la plante, ou dans I'animal de meme espece qui 1 a 

 produit." — Nov.velles Observations, p. 169. 



" Les naturalistes ont generalement cru que les animaux mieroscopiques ^talent engen- 

 dr^s par dcs ocufs transportes dans I'air, ou deposes dans des eaus dormautes par des 

 insectes Tolans." — Ibid. p. 176. 



