FROM SIMPLE PERCEPTIBLE MATTER. 557 
soil for their growth, permit us to have before our eyes, in our room, the 
eycle 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 accurate observations. 
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- 
ealled 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 very 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, considering the numerous frequently crude animal 
aliments beginning with the chyle and the milk, than the relative rarity 
of those parasitical organisms, considering their enormous predisposition 
to increase by eggs. We seldom find, indeed, animal bodies or human 
