FROM SIMPLE PERCEPTIBLE MATTER. 557 



soil for their growth, permit us to have before our eyes, in our room, the 

 cycle of the development of these forms. 



Continued investigations of the most minute organized beings have 

 of late more and more confirmed me in the opinion that, not only in all 

 these forms, besides the supposed generatio spontanea, a cyclical deve- 

 lopment may be ascertained by examination, but they even compel me 

 to declare that all observations and experiments in support of the gene- 

 ratio spontanea are by no means sufficiently careful and faultless to 

 produce conviction ; and that the idea of a generatio primitiva of or- 

 ganic bodies, to have the value of an ascertained fact, must be proved 

 afresh by more acc-urate obser\'ations. 



2. Intestinal Worms. — The idea of the generatio primitiva being 

 founded not on the fungi and moulds alone, but more particularly on 

 the inexplicable origin of the intestinal worms and the infusoria, I at a 

 subsequent period especially directed the whole of my attention to these 

 forms. In the years 1820 to 1826, and in 1829, I collected, in my 

 voyages in Africa, Western Asia, and Siberia, as many geographical ob- 

 servations as possible of all the smallest existing organisms ; and by 

 means of the great quantity of my unbiassed observations pursued for 

 so many years under very different circumstances, I became more and 

 more disinclined to the notion of the generatio spontanea, as I acquired 

 a far clearer insight into the highly perfect organization of these so- 

 called organic ultimate forms, molecules, or minutest organic beings, 

 which has disproved the necessity of their primitive origin, and opposes 

 to it possibilities and realities entirely different. 



On examining the intestinal worms, I everywhere found the entire 

 structure of almost all these animals so decidedly adapted to an oviparous 

 propagation, that I should rather be led to ascribe the apparent anomaly 

 and mysteriousness in their origin to their essential relation to the inner 

 parts of living animal bodies to which they are limited, and the great 

 difficulty of the direct observation of their cyclical development arising 

 from that cause, than to an entirely peculiar power of nature, which is 

 in action there alone where human investigations are excluded and the 

 senses do not reach. Organs of copulation and production, clearly de- 

 veloped and never deficient, and the development of which surpasses 

 for the most part those of other organic systems, plainly point in the in- 

 testinal worms to a predominant cyclical development, in the same man- 

 ner as it is exhibited in the larger organisms, and make their generatio 

 primitiva verj' improbable, for which indeed there is no other argument 

 than the difficulty of observation. The occurrence of intestinal worms 

 in the interior of organic bodies does not appear to me more remarkable 

 or incomprehensible, consitUsring tlie numerous frequently crude animal 

 aliments bc-ginniiig with (lie chyle and the milk, than the relative rarity 

 of those parasitical organisms,' cuiisidering their enormous predisposition 

 to increase by eggs. Wc seldom find, indeed, animal bodies or human 



