573 



ENTOZOA. 



ENTOZOA. 



674 



genera : they have no intestinal canal, and the organs of generation 

 of the two sexes co-exist in the same individual. This is a very 

 natural order. 



Order IV. Acanthocephala, (from fucavOa, a thorn ; and Ke<f>oA}j, the 

 head), Hooked- Worms. Characters : Body elongated, round, sub- 

 elastic ; the anterior extremity or head has a retractile proboscis, 

 furnished with hooks or spicula, arranged in rows. They have no 

 intestinal canal, but distinct genital organs, and a separation of the 

 sexes. This is a very natural group, and includes the most noxious 

 of the internal parasites ; there is only one genus, and fortunately no 

 Bpecies is known to infect the human body. 



Order V. Ntmaloidea. (from rtina, a thread, and ei5i>s, form), Round- 

 Worms. Characters : Body cylindrical, elongated, and elastic ; struc- 

 ture very complicated, there being a true intestinal canal, terminated 

 by a distinct anus. The mouth, by its varieties, affords generic 

 characters ; the sexes are distinct ; the females, which are longer than 

 the males, being for the most part oviparous. They constitute a very 

 natural order. 



Having given the above brief view of the orders into which the class 

 Entozoa is divided, with the leading or- characteristic differences in 

 their form and organisation, we wUl now enumerate the principal 

 genera contained in each group, and make a few observations on some 

 of the most interesting species. Following the order of classification, 

 we must commence with the most simple group, the Cystica ; and 

 here the first parasite which attracts our attention is the common 

 Hydatid, which consists of a globular bag, composed of condensed 

 albuminous matter of a laminated texture, and contains a limpid 

 colourless fluid. No head or appendices of any sort being attached 

 to it, it is appropriately denominated an acephalocyst, that is, a head- 

 legs cyst. This genus was established by Linnaeus, who regarded as 

 animals those productions which before his time had been considered 

 simply as cysts. Considerable diversity of opinion still exists as to 

 their nature, and it is impossible to determine whether an hydatid is 

 an animal or not, till we can agree what is the definition of an animal : 

 if an animal must have sensation and motion, this is not one, as the 

 best observers agree that the acephalocyst is impassive under the 

 application of stimuli of any kind, and manifests no contractile power, 

 either partial or general. If an animal is characterised on the other 

 hand by independent existence merely, the hydatid is one ; and as 

 such we shall regard it, for it is certainly an independent organised 

 being, growing by intrinsic power of imbibition, and reproducing its 

 species by gemmation ; the young are developed between the layers 

 of the parent cyst, and thrown off internally or externally, according 

 to the species. It is a being certainly far inferior in the scale to the 

 Cyiticercut, but still not the less an independent creature. Its struc- 

 ture is very similar to that of some of the lowest forms of Algce in the 

 vegetable kingdom, as the Protococcut nivalu, or Red Snow, of the 

 arctic regions, which consists of simple and minute vesicles, which 

 propagate then? kind by gemmules developed from the external 

 surface of the parent. Acephalocysts have been found in almost 

 every structure and cavity of the human body, but particularly in 

 the liver, uterus, kidneys, and cellular tissue. The species which 

 resides in man is called A. mdogena, the Pill-Box Hydatid of Hunter, 

 from the gemmules being detached from the internal surface of the 

 cyst ; and it is thus distinguished from those of the ox and other 

 ruminating animals, which are exogenous, or have the gemmules 

 excluded from the external surface. 



2. The next genus is JScchinococcue, which, as the name implies, 

 is a round body covered with asperities. The . hominii, or Many- 

 Headed Hydatid, of the Germans, occurs in cysts in the liver, spleen, 

 omentum, and mesentery ; the cyst, which is externally yellow and 

 coriaceous, is unprovided with head or mouth, and contains minute 

 bodies, which are described as possessing the armed and suctorious 

 head characteristic of the Ctenuri and Cysticern. From observations 

 made on another species, the E. reterinorum, found in animals, the 

 particles adhering to the internal surface of the cyst being examined 

 with a microscope, appeared to be minute animalcules, moving about 

 by means of external vibratile cilia, having an orifice at each extremity 

 of the body, and the centre occupied by large globular stomachs. 

 These little animals are the Echinococcus. The following account of 

 these bodies is from the abstract of a paper read by Mr. T. H. Huxley 

 before the Zoological Society. After describing the cysts he says : 



" The contents of the large cysts were free Echinococci and 

 secondary Ecldnococcut cysts, contained in a clear fluid. The former 

 were alive, and exhibited' distinct contractile motions. Attention was 

 drawn to two important points in their structure ; firstly, that the 

 well-known oval corpuscles were not calcareous, inasmuch as they 

 were rapidly dissolved by acetic acid without effervescence, and were 

 considerably acted upon by ammonia. The author supposed that 

 they were albuminous, and that both in these and the Tirnus the 

 conversion into calcareous substances is an effect of degradation ; and 

 he pointed out their relations with the solid bodies in the integu- 

 ment of the Turliellaria, and with the so-called thread-cells of these 

 and the Polypa ; secondly, that the peculiar wavy cilia characteristic 

 of a water vascular system could be seen in motion in the living 

 "/coca. The cilia were described by Lebert in 1843, but the 

 discovery seems to have been forgotten. It is however a point of 

 great importance now that the existence of similar cilia in a definite 



water vascular system has been demonstrated in the other Cestoid 

 Worms. The proper wall of the cyst (as distinguished from the lami- 

 nated capsule) was traversed by a network of anastomosing vessels, to 

 the points of union of which the fixed Echinococci were attached, the 

 cavity of the pedicle of the latter appearing to be continuous with 

 that of the vessels. It is in the cavity of the pedicle that Virchow 

 observed cilia. The secondary cysts varied in size from l-100th to 

 l-30th of an inch. The contained Echinococci were always of about the 

 same size, and all the smaller secondary cysts possessed from one to 

 four Echinococcus heads attached to their outer surface. The wall of 

 the secondary cysts contains vessels like those of the primary one. 

 In the larger cysts the external heads were found gradually disap- 

 pearing until they were quite smooth externally. When the secondary 

 cysts were burst, their membrane continued to connect the heads and 

 formed the pedicle described by various authors. The formation of 

 secondary cysts takes place thus : Echinococcus heads are formed 

 over the whole inner surface of the cyst ; this then becomes raised 

 up at one spot by the development of Echinococcus heads outside it 

 also, and gradually projecting inwards, and acquiring a narrower and 

 narrower pedicle it eventually falls into the cavity of the cyst as a 

 free secondary cyst. The external heads of the secondary cyst (inter- 

 nal of the primary cyst) then gradually disappear, the internal ones 

 (external of the primary cyst) remaining entire and in a normal state. 

 The process is not essentially different from the ordinary germination 

 of a Tcenia, or Cysticercus. The author then endeavoured to show 

 that the Echinococcw is nothing but the ' Scolex-form ' to use Van 

 Beneden's term of a Tienia retracted within itself, then greatly 

 dilated, and developing Echinococcus heads from its inner and outer 

 surfaces, which are however, like those of a serous sac, in reality both 

 outer. It is the extreme result of modifications similar to those 

 already undergone by the Taenioid type in Ccmunts and Cysticercus. 

 The conclusion thus drawn on anatomical grounds is strikingly con- 

 firmed by the result of the recent experiments of Von Siebold, who 

 fed young puppies on milk containing Echinococci, and after a short 

 time discovered Tienia in their intestines." 



3. Anthocephalut is the next genus. It occurs in fish, in the liver, 

 mesentery, and peritoneum, and within hydatids in the viscera. Each 

 animal exists solitarily in a double bladder, of which the outer layer 

 is hard and elastic, the inner more thin and delicate. The body is 

 long, flat, terminated behind by a caudal vesicle, and in front by a 

 head with two or four fossa;, and four probosces furnished with 

 spicular processes. 



4. Canwu*. This has the terminal cyst common to many bodies 

 and heads; the former are elongated, flattish, and wrinkled; the 

 latter are furnished with a rostrum, on which there are hooks and 

 suckers adhering in greater or less number to the surface of a bladder 

 filled with fluid. The best known species is the C. cerebralis, com- 

 monly developed in the brain of sheep, and giving rise to the disease 

 called the Staggers. 



5. Cysticercue. Here there is a dilated cyst forming the termination 

 of a single entozoon : the head has four suckers, and a rostrum 

 furnished with recurved processes or hooks. Of this genus one 

 species is known to infest the human subject, the C. celluloate. It is 

 developed in the interfascicular cellular tissue of the muscles, and 

 is invariably surrounded by an adventitious capsule of condensed 

 surrounding substance. This entozoon occurs much more rarely in 

 this country than on the Continent. It is not confined to the muscular 

 structures, for several individuals have been detected in the anterior 

 chamber of the eye, where they may occasion so much irritation and 

 inflammation of the organ as to require extraction, which occurred 

 some years ago in a case in the Glasgow Ophthalmic Infirmary. These 

 parasites also occur in quadrupeds, particularly the hog, giving rise 

 to that state of the muscles which is called Measly Pork. 



Of the Cestoid order of Entozoa Rudolphi has described 8 genera, 

 two only of which contain each a single species that infest the human 

 body : 



1. Bothriocephaliu, the species of which occur frequently in fishes 

 and birds, in the branchieo, oesophagus, pyloric appendices, intestines, 

 and abdominal cavity. The one which affects the human subject, 

 B. latue, or Tienia lata, rarely falls under the observation of the 

 English entozoologist, but is common in the intestines of man in 

 Switzerland, Russia, parts of France, &c. It may be distinguished 

 from the Tcenia solium by the form of the segments, which are 

 broader than they are long, and by the position of the genital pores, 

 which are on the under surface of the body, instead of at the sides ; 

 the head is also very different, for instead of having four round 

 oscula, characteristic of the true Tieniie, there are two lateral longitu- 

 dinal fosstc or bothria. 



2. Tienia. This genus has the body flat, long, articulated, with four 

 suckers on the head. It occurs in the intestines, biliary ducts, gall- 

 bladder, and liver of vertebrate animals. The T. eolium, common 

 Tape-Worm, inhabits the human intestines, but not with equal 

 frequency in all countries, though its distribution seems to be much 

 more extensive than that of the JSothriocephalus lalus. It occurs in 

 England, Holland, Germany, Sweden, Italy, Greece, and most coun- 

 tries in Europe, and also in Egypt and the East ; and in all these 

 situations the other genus is comparatively rare. 



The delicacy of their structure, and their so seldom being obtained 



