80 



STERELMINTHA. 



circumstances, deprived of all power of locomotion, as is gene- 

 rally a necessary consequence of the localities in which they are 

 found, debarred from the influences of light, and absolutely de- 

 pendent upon the fluids which bathe their bodies for nutriment, 

 the entozoa have little occasion for that elaborate organization 

 needful to animals living in immediate communication with exter- 

 nal objects. 



We find therefore, among these creatures, some whose structure 

 is more simple than that of any other animals, in adaptation to the 

 circumscribed powers of which they are capable. Yet, however ap- 

 parently insignificant some may appear from their diminutive size, 

 they not unfrequently become seriously prejudicial to the animals 

 in which they are found, by the prodigious numbers in which they 

 exist, or from their growth in those organs more especially essential 

 to life, and not a few of them from their dimensions alone some- 

 times prove fatal. The annexed figure (Jig. 32) represents a 

 Ligula developed in the abdominal cavity of a Fig. 32. 



fish. There are probably no races of animals 

 which are not infested with one or more species 

 of these parasites, from the microscopic infu- 

 soria up to man himself, and sometimes several 

 different forms are met with in the same spe- 

 cies, to which they would appear to be peculiar, 

 and even in some cases the entozoa would 

 seem themselves to enclose other species para- 

 sitically dwelling in their own bodies. Neither 

 is their existence confined to any particular 

 parts ; they are met with in the alimentary 

 canal, in the liver, the kidneys, the brain, the 

 arteries, the bronchial passages, the muscles 

 and cellular tissue, and in fact in almost all the 

 organs of the body. 



(109.) It would appear that some of the ordinary secretions of ani- 

 mals are, when in a healthy state, naturally inhabited by innumerable 

 active beings, scarcely equalling in bulk some of the most minute 

 infusoria, and consequently requiring the highest magnifiers to 

 detect even their presence. The best known of these are found in 

 the seminal fluid, and of their size the reader may form some judg- 

 ment by the following calculations upon this subject. Reil esti- 

 mated the length of those found in man at the 3 0*0 o o P ar t of an 

 inch, or at the 25,000th part of a line, and their breadth at the 



