FROM SIMPLE PERCEPTIBLE MATTER. 559 



organs of the larger animals is also found to exist. There are very often 

 observed in animal dissections a small number of full-grown worms, 

 filled with an innumerable quantity of eggs without any young in their 

 proximity ; and I was often astonished to find in the considerable num- 

 ber of my dissections of animal bodies (I have brought from Africa 

 alone intestinal worms of 196 species of animals, all of which I have 

 myself dissected, and of some from 40 to 50 individuals,) only a few 

 alive, although these were completely filled with eggs. Thus from la- 

 borious observations this opinion has become more and more firmly 

 fixed in my mind, that it is much more astonishing how the great fe- 

 cundity of the Entozoa should be so limited by the living organs, than 

 that it should be possible that living worms should inhabit them, and, 

 considering their diffusion, escape observations which are generally su- 

 perficial. The Epizoa present to the observer quite a different propor- 

 tion, although these can for the most part be limited voluntarily by the 

 animals. The circumstances favourable to their cyclical development in 

 most cases overcome those which limit it ; and a careful observer might 

 follow with ease the formation and development of their innumerable eggs. 

 It is not the small size of the Entozoa which forms the difficultj^ but 

 solely their inaccessible station in the interior of living animal bodies. 

 3. Infusoria. — Of an entirely different nature is the difliculty of ob- 

 servation in the Infusoria, the third strong hold of the generatio cequi- 

 voca: it lies in their minute size. Observations of Infusoria, which 

 I pursued with great zeal and repeated on every occasion, showed me 

 the necessity of a more definite determination of their forms, which I 

 endeavoured to acquire by drawings and measurements of them. These 

 severe and often-repeated investigations of individuals enabled me fre- 

 quently to recognise the most decided traces of a higher internal organi- 

 zation than had previously been ascribed to them. In the year 1819 

 I had already observed that the motion of the zoological monads {Monas 

 pulvisculus) was by no means a mere rolling effected by a change of 

 the centre of gravity, as it was thought to be ; but I perceived, fi'om 

 the throwing off of very minute particles of the dirty water, and from 

 an apparent whirling at the anterior part of the animalcule, the presence 

 of oarlike cilia, which at times even became visible. Some of these ob- 

 servations I made knoMU in 1820, in an Appendix to a Memoir by my 

 friend Friederich Nees von Esenbeck in the Regensburg Botanical Jour- 

 nal, part ii. p. 535. My friend and subsequently fellow-traveller Dr. 

 Hemprich often witnessed my observations and experiments, and has also 

 given, in his Grundrisse der Naturgeschichte, 1820, p. 289 to 291, a sum- 

 mary account of what I had ascertained at that time (see preface, p.viii.). 

 I was not then myself desirous of making publicly known any of those 

 observations, because I saw on the one hand that they were capable of 

 being carried to much greater perfection, and on the other hand, I pos- 

 sessed at that time only a very incomplete thirty-shilling wooden com- 



