ENTOZOA. 57 



LECTURE IV. 



ENTOZOA. 



The ancient philosophers styled man the microcosm, fancifully con- 

 ceiving him to resemble in miniature the macrocosm or great world. 



Alan's body is unquestionably a little world to many animals of 

 much smaller size and lower grade of organisation, which are 

 developed upon and within it, and exist altogether at the expense of 

 its fluids and solids. 



Not fewer than eighteen kinds of parasitic animals have been 

 found to infest the internal cavities and tissues of the human body ; 

 and of these, at least foui'teen are good and well established species of 

 Entozoa. 



Hippocrates and Aristotle had distinguished the hnman intestinal 

 worms by the names of " Helminthes stronguloi " and " Helminthes 

 plateiai ; " but the study of these parasites in general has been re- 

 served for recent times. Since Linnaeus the stimulus which that 

 great master gave to every branch of Natural History has been in no 

 department more potent than in encouraging researches into the 

 before neglected field of the Internal Animal Parasites. 



To the labours of Goeze*, Zederf, Bremser|, and, above all, to 

 those of Rudolphi §, we are indebted for our knowledge of these 

 animals as an extensive class, which Rudolphi has characterised, 

 under the name of Entozoa, as white-blooded worms without respira- 

 tory organs, and (but less accurately) without nerves. 



The number of these parasites may be conceived when it is stated 

 that almost every known animal has its peculiar species, and generally 

 more than one, sometimes as many as, or even more kinds than, infest 

 the human body. 



There are few common and positive organic characters which can 

 be attributed to this very extensive and singular group of animals ; 

 they have generally a soft, absorbent, colourless integument, which in 

 a few species is armed with spines. That the integument should be 

 uniformly white or whitish might, a priori, have been expected of 

 animals which are developed and exist in the dark recesses of other 

 animal bodies. The mature ova are almost the only parts which 

 naturally acquire a distinct colour ; and the subtransparent body some- 

 times derives other tints from the accidental colour of the food. Ex- 

 cluded also by the nature of their abode from the immediate influence 



* XLVIIL t "^-^ t L. and LI. § XLVL and XLVEL 



