BONNET 289 



which, when cut up, form as many animals as there 

 were pieces.^ 



Bonnet remarked that his worm (Lumbriculus) 

 occasionally budded out a second head; if he had 

 happened to study Nais instead (as is often alleged), it 

 is probable that he would have observed the frequent 

 formation of a zone of division, and the spontaneous 

 segmentation of the worm into two complete individuals. 

 Both artificial and spontaneous fission were observed in 

 Nais by Eoesel ^ a few years later. 



Bonnet's once-celebrated theory of emhottement may 

 be sufiiciently discussed in a few words, since it has long 

 ceased to occupy the thoughts of biologists. The facts 

 on which it rested were these : — insect-larvae and pupae 

 often contain eggs; aphids can reproduce for many 

 successive generations without fertilisation ; Malpighi 

 had found a rudimentary chick in an egg which had 

 never been sat by a hen {supra^ p. 159). From these 

 facts Bonnet drew very wide conclusions. All female 

 animals, he said, whether fertilised or not, contain 

 embryos, which are capable of development, and enlarge 

 simply by absorption from the surrounding tissues. The 

 embryo is " preformed," and exists before the body by 

 which it ultimately becomes enclosed. It was easy to 

 trace in imagination the invisible rudiment to the Qgg, 

 to the parent, to the grandparent, and so on ; Bonnet 



^The preface to Reaumur's sixth volume (p. Ivi), published three years 

 before the Traits d'lnsectolorjie, makes this clear. Wo have also the testimony 

 of Trembley : — "M. Lyonet, qui est le premier qui ait coupd des vers, et qui 

 ait vu chaque partie devenir un ver parfait, &c." {Polype d'tau dowe, p. 223). 

 It is not easy after this to understand Bonnet's account of the matter, nor his 

 assurance that he had no direct knowledge of Lyonet's experiments when the 

 Traits, was sent to the press (Preface to TraiU d'Insectologie, Vol. II). No 

 doubt Lyonet had Bonnet in mind when he complained of those who had 

 anticipated him by publishing the results for which he had laboured (Profaoo 

 to TraiU Anat. de la Chenille, &c.). 



'^ Inaecten-Belustigungen, Vol. Ill, pp. 567-684 ; pi. 92-8. 



T 



