in 



UTOBQA. 



F.NTOZOA. 



571 



parasitic position. Nevertheless, although th* condition* of life are 

 necessarily ever present in living being*, yet theae frequently do not 

 contain parasites. There are many circumstances, beside* those 

 os*imti*l to life in general, which influence the existence or non- 

 existence of nioh form*. One of the most important of these circum- 

 stances U the oonreuienoe or ease of aocei* or of entrance to the living 

 body infected. Within the living cloud organic cell parasite* very 

 rarely if ever exist, because it U liquid matter only which can endos- 

 mose through cell membrane, and therefore solid genus cannot enter, 

 and hence the unfrequency of true k'ntozoa in vegetables. Entozoa 

 may and do penetrate through liviug tissues, but it is entirely by the 

 mechanical process of boring. 



" The intestinal canal of animal* is most frequently infested by 

 entoparasites on account of the ease with which their germ* enter 

 with the food. 



" Aquatic animal* are more troubled by Eutozoa. than those which 

 are terrestrial, because the water affords a better medium of access 

 than the air. 



" Terrestrial animals, on the other hand, are more infested by ecto-' 

 parasites because their covering of hair, wool, and feathers, is more 

 favourable to their protection and reproduction. A low degree of 

 organic activity and slowly digestible food favour the development of 

 ectoparasites, and hence they are more frequent in the relatively 

 sluggish //rrltirora than in the t'arnirora. Comparatively indigestible 

 food, and such as contains but a small proportion of nutritive matter, 

 from its long retention in the alimentary canal, favours the develop- 

 ment of entozoic and entophytic germs more than that in which the 

 contrary conditions prevail. Animals subsisting upon endosmosed 

 nieces of the tissues of other animals and of plants are rarely infested 

 by parasites, as in the case of the hemipterous insects, aphides, ftc., 

 because such food is necessarily free from parasites or their germs. 

 EnlooM themselves, on this account, are not infested. 



" On the other hand, if the liquid food be open to the air, parasitic 

 germs may be readily introduced into the animal, as in the case of 

 the common house-fly, which often contains myriads of a species 

 of Bodo. Food swallowed in large morsels favours the introduction 

 of attached parasites ; hence these are frequently found in reptiles, 

 and even in birds, which are among the Vcrttbrata of the highest 

 organic activity. 



" Animals of feeble organic activity, using solid food, which is very 

 slowly digested and contains little nutriment, are rarely free from 

 parasites. This is the case with the coleopterous insect Papalus and 

 myriapod Jalia. Cooking food is of advantage in destroying the germs 

 of parasites, and hence man, notwithstanding his liability to the 

 latter, is less infested than most other Mammalia. Did instinct 

 originally lead him to cook his food to avoid the introduction of 

 parasites? 



"Entozoa are more abundant than Entophyla [ENTOPHYTA], because 

 the power of voluntary movement favours them in their transmigra- 

 tions, and renders them less liable to expulsion from the intestinal 



Although it is now a general opinion that the Entozoa are intro- 

 duced from without, it is very certain that with some it cannot be in 

 their adult form. From some recent researches it appears that, like 

 many of the Radiate Animals, the Entozoa assume various forms after 

 escaping the egg before they attain their final condition. Steenstrup, 

 in his ' Alternation of Generations,' has shown that Entozoa belonging 

 to the Tn-matode forms, pass through various conditions of existence. 

 Thus he has traced the species of Diitoma in the higher animals to 

 the various forms of Cercaritr. Mr. Busk has also pointed out 

 (' Transactions of Microscopical Society,' vol. ii.) the probability that 

 one of the Nematoid Worms, the Filaria iftdintntit, the Guinea- 

 Worm, passes through other forms before it penetrates the human 

 body, and assumes its characteristic form in the human skin. With 

 regard to the Entozoa of the higher animals, their eggs seem to be 

 produced in that position, but not to be perfected where they have 

 been generated. It has been shown that the ova of the Jint/irio- 

 cepkalut, an entozoon found in birds, never come to perfection unless 

 the ova are first swallowed by the Stickleback, which being eaten by 

 the bird, the entozoon takes the opportunity of assuming its proper 

 form. The Gordiiu, or Hair- Worm, deposits its eggs in water, but 

 the eggs are not developed in this position ; they are first swallowed 

 by insect*, and in this position the egg is hatched, producing the 

 Gordiiu, which becomes impregnated, and escapes from the insect 

 into waters where it deposits its egg*. The ova of a species of Tnnia, 

 Tape-Worm, when swallowed by the rat or mouse, will not produce 

 perfect tepe-wonns in the inside of these creatures, but if they are 

 eaten by the oat or dog, then the perfect tape-worm is produced. 

 [GKXERATIOX, ALTKRSATIOSS or.] 



According to the derivation of the word Entozoa and the definition 

 which we have given of it, this term should include every living 

 creature found in the body of another (which has not been introduced 

 from without) : therefore the small microscopic animalcules detected 

 in the semen of animals, called Spermatozoa, come under this head ; 

 and in a very able paper on the ' Entozoa' by Professor Own. 

 find them placed accordingly in this class, only situated in a separate 

 group, denominated /'/,-.',;, //,>/,,/. and divided from the animals 

 forming the class Enlo-.oa of Kudolphi. These minute beings, which, 



from their sixe and organisation, rank with the assemblage of animal- 

 cules which are collected under the head /n/iuorui in the ' Ki'gne 

 Animal,' have been detected in the secretion of the testicles of 

 various mammiferoo* animals arrived at maturity. When a drop of 

 the secretion is expressed from a divided vas deferens shortly after 

 death, and examined with a microscope, after being diluted with 

 water, it is seen to be filled with minute beings resembling tadpole*, 

 and swimming about in various directions, with different degrees of 

 velocity, guided by the inflection of a slender tail It has been 

 doubted whether these are animated beings at all, or are to be 

 considered as analogous to the moving filaments of the pollen of 



Cite ; but leaving this undecided, we may proceed to state that the 

 y is always of a compressed form, which will distinguish these 

 animalcules from the vegetable Infiuvria, in which the body is 

 always ovoid or rounded. With regard to their organisation, no 

 itlimontary canal or gastric cavities have been detected, nor organs of 

 generation ; they are said to be fissiparous, the body and tail 

 spontaneously dividing, and forming two independent beings. The 

 shape of these zooeperms differs in different animals, the large end, 

 or body, being bigger in proportion to the tail in some than in others, 

 and their size not being always in relation to that of the animal to 

 which they belong : thus those of the rabbit are nearly aa Urge as 

 those from the bull. 



In the present group are also included those minute internal 

 parasites which have been detected in the bodies of many of the 

 Entozoa themselves, and which, from their external form, are referrible 

 to the Infusoria. 



The Trichina tpiralii, an entozoon found inhabiting the muscles of 

 the human subject, has been placed by Professor Owen, who first 

 described it, with the preceding animalcules; but further observa- 

 tions on its organisation have discovered a complexity of structure 

 which qualifies it to occupy a place in the highest instead of the lowest 

 group into which the present class of animals is divided. 



Cuvier divided the tnie Entozoa into the ' cavitaires,' or those which 

 have an abdominal cavity, and a distinct intestinal canal within it, 

 and the ' pareuchymnteux,' or those in which no intestinal tube is 

 traceable, and which for the most part consist throughout of an homo- 

 geneous structure ; but this classification is anything but a natural 

 one, as worms the most dissimilar in their general appearance are 

 here promiscuously congregated together. Professor Owen, in the 

 article which we have before alluded to (in the ' Cyclopssd. of Anat'), 

 has adopted the arrangement of Cuvier, only inventing new Latin 

 names derived from the Greek, instead of the French terms : thus 

 he denominates the ' pareuchymateux ' Sterelmintha, from clmine, 

 'a worm," and stereos, 'solid; and the 'cavi tains' Coclelmintha, 

 from elmiiu, and ctelot, ' hollow.' Zeder laid the first foundation of a 

 good classification of these animals, dividing them into five classes, 

 afterwards called families, at Itudolpbi's suggestion ; and these were 

 again subdivided into genera and species. Kudolphi himself doubted 

 the possibility of ever reducing all the species of Entozoa to absolutely 

 natural and well-defined families, but as Zeder's system seemed the 

 most perfect, he has adopted it for his own ; and it does not seem 

 that we can do better than follow the arrangement of this great 

 entozoologist in the present article. 



According to this classification the Entozoa are divided into five 

 orders, or families, the timatoidea, Acantkocephala, Trematoda, 

 Cettoidea, and Cyttica. The only point in which we shall depart from 

 this arrangement will be, that, instead of commencing with the most 

 perfect, and descending to the most simple, we shall begin with the 

 lowest in the scale of organisation, and ascend to those possessing the 

 most complicated structure, as this U most in accordance with the 

 laws of the animal kingdom. 



Order I. Cyttica (from Kihrrit, a bladder), Hydatids. The characters 

 are : Body flattish, or roundish, and terminating posteriorly in a 

 transparent cyst filled with pellucid fluid, which is sometimes common 

 to many individuals ; the head is retractile, and provided with pits 

 two to four in number, or four suckers and a circle of booklets, or 

 with four unarmed or uncinated tentacles. The organs of generation 

 and nutrition are unknown. This is not a very natural family, the 

 species being closely allied to those of the next order in the structure 

 of the heads ; and the Ecfiinococcus, or Granular Hydatid, though 

 referred to it, is not hollow. 



Order II. Cettoidea (from KHTTOS, a band ; and tTSos, form), Tape- 

 Worms. Characters : Body elongated, flattened, soft, continuous, or 

 articulated, furnished with lateral or marginal pores, and erectile 

 papillic passing through them, supposed to be the male organs of 

 generation. Head generally provided with two or four pits, or 

 suctorial orifices, and sometimes with four retractile, unarmed, or 

 uncinated tentacles ; but the head is so dissimilar in different genera, 

 mid their shape varies so much, that they do not form a very natural 

 family. There i* no trace of intestinal canal ; unless the vessels 

 proceeding from the suckers be considered as such. In some 

 species nutrient vessels and ovaries are to be seen. They are all 

 androgynous, 



Order III. Trematoda (from TJMJ/IO, a foramen), Fluke- Worms. 

 Characters': Body soft, rounded, or flattened. Head indistinct, with 

 a suctorial foramen ; one or more suctorial pores on the under surface 

 of the body, which furnish the grounds for their subdivision into 



