ACANTBOCKPHALA. - 



-ENTOZOA.- 



-Cestoidea. 



305 



anterior, containing the mouth, the other imperforated, 

 and situated on the ventral surface hetween the middle 

 and the first sixth of the length of the body. The 

 intestine is divided into two branches. 



OuDER IV.— ACANTHOCEPHALA {Hooked 



Worms). 



Tlie worms be'onging to this order, the Hooked 

 Worms, as they are called, are slender, more or less 

 elongated, of an ovoid-oblong or cylindrical form, and 

 provided witli a retractile proboscis, armed with hooks 

 or spines arranged in rows. They appear to have 

 neither mouth nor digestive tube, but take their nourish- 

 ment by absorption. The sexes are separate, and the 

 females are oviparous. 



This order contains only one genus, Echinorhynchus, 

 the species of which are generally of a round or cylin- 

 drical form, and in some instances attain a considerable 

 length, tliough in others the body is shortened to a kind 

 of sac. The hooked proboscis is extensile, club-shaped, 

 or nearly globular, and the spines are sometimes very 

 numerous, being arranged in some species in as many 

 as sixty transverse rows. They are chiefly found in the 

 alimentary canal of vertebrated animals, and attach 

 themselves to the coats of the intestines by means of 

 the hooked spines on the proboscis. It is princijially 

 in Ampliibia and Fishes that they are found, but occa- 

 sionally they occur in Mammalia. 



Ordicr v.— CESTOIDEA {Cestoid Worms). 



This order includes a variety of worms, which accord- 

 ing to Rudolphi and his followers, made a separate 

 order by themselves, under the name of Cystic woims 

 {Cyslica), but which are now better understood, and 

 proved to be the immature or undeveloped forms of the 

 Cestoid worms. 



The order Cestoidea may be briefly characterized 

 thus : — Worms with a soft body, generally flattened or 

 band-shaped, and formed of numerous joints. They 

 possess neither intestine, mouth, cor vent. They have 

 ordinarily a head furnished with two or four suckers 

 or small pits which are muscular, very contractile, 

 and frequently armed besides with booklets disposed 

 in a terminal crown, or in pairs in front of each pit, or 

 very numerous upon four or two retractile proboscides. 

 The genital organs of both sexes are united, either on 

 a single joint or on distinct joints {;^CestoiJca). Some- 

 times from an arrcs* of development, there are no 

 genital organs, and then frequenily the body of the 

 worms is terminated by an isolated vesicle, either single 

 or common to several [=:^Cyxtica). 



Genus T.snia, or Tape-worm. — The worms belong- 

 ing to this genus are white, very long, and flat. The 

 body is composed of a great number of joints or 

 segments very variable in shape and size, and verj- 

 contractile. The head is round or tetragonal, and is 

 surrounded by four roimd, muscular, very contractile 

 suckers. In the centre of tliis head there generally 

 issues a proboscis of a greater or less length, and com- 

 pletely retractile into a muscular receptacle. Tliis 

 proboscis is, in some of llie species, naked or unarmed, 

 Vol. II. 



but in a great proportion it is surrounded with booklets 

 forming one or two rows. The first joints of the body 

 are generally very short and numerous ; the middle ones 

 are generally broader than long, but of variable shape, 

 and provided with more or less distinct genital organs ; 

 and the last are filled with ripe ova and then often 

 become longer than broad. The genital organs, com- 

 plete in each joint, have the orifices situated at the two 

 opposite sides of each in some, or at one side only in 

 others ; and in this case they are either always or gene- 

 rally on the same side (unilateral) or they are alternately 

 on one side or the other. The last joints are capable 

 of being detached and living separately, and each joint 

 being a perfect animal as far as the generative appara- 

 tus is concerned, the propagation of the species is capable 

 of being carried on to a very great extent. The Tape- 

 worms are fomid living in the intestinal canal of verte- 

 brated animals, more especially Mammalia and Birds. 

 Of late years some exceedingly interesting and very 

 curious facts with regard to the development of Tape- 

 worms have come to light, and the extraordinary trans- 

 formations of Cystic worms into Tceniie have been tlie 

 means of enabling naturalists to do away with the 

 former as a distinct order altogether. Siebold appears 

 to have been the first who advanced the statement, that 

 certain Cystic worms were nothing but stray Tape- 

 worms which had become vesicular. The Cystic worms 

 are generally small creatures contained in a cyst, having 

 the head furnished with a crown of booklets, and the 

 body terminated by a bottle-shaped vesicle filled with 

 liquid. They are always destitute of genital organs. 

 By a series of experiments made, Siebold ascertained 

 that if the Cystic worms which inhabited the body of 

 a mouse or rabbit, for instance, were swallowed by a 

 dog, these Cystic entozoa of the rodent become in a 

 short time, in the intestines of the carnivorous animal, 

 a perfect and full3'-developed Tccnia. A species of 

 C3'stic worm (the Cysticercus fascicularis) infests the 

 liver of rats and mice. Having previously ascertaineil 

 that certain specimens of these worms were contained 

 in the liver of a mouse, the animal was given to a cat. 

 Several animals were thus fed, and by killing them at 

 certain intervals one after the other, the transformation 

 was seen to take place. The liver of the mouse was 

 digested in the stomach of the cat, but the Cysticaxus 

 was left unharmed. It soon loses its terminal or 

 caudal vesicle ; and finding in the chyme of the 

 stomach and small intestines of the cat a suitable 

 place for furllier development, it speedily assumes 

 the articulated form of a Tape-worm. When fully 

 developed, the species was ascertained to be the 

 common Tape-worm of the cat, the Tcenia crassicoUig. 

 Encouraged by the success of this experiment, Siebold 

 next tried it with a species which is found living in 

 cysts in the coats of the intestines of the rabbit, the 

 Cysticercus pisiformis. Several dogs were fed with 

 animals infected with these cystic worms, and upon 

 killing the.se dogs at intervals of from two hours to 

 eight weeks after being fed, lie found these little para- 

 sites of the rabbit gradually assuming the form of iho 

 common Tape-worm of the dog, Taiiia scrrata. Fir-st 

 he found the cysts disappear, then the terminal vesicle 

 becomes absoibed, the worm then quickly begins to 



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