CLASS E NTOZOA. I. \TESTINAL- WORMS. CLASS ACALEPHA. SEA-NETTLES. 



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CLASS XII. E NTOZOA. INTESTINAL-WORMS. 



RUDOLPHI applied the name Entozoa to those Animals which live within the internal parts of others, and divided them, from their form, 

 &c., into the Cystic, Cestoid, Trematode, Acanthocephalous, and Naematoid Orders. These, however, have been reduced by 

 Cuvier to two, 1st, the Parenchymatous, including Rudolphi's first four, of which the body is filled with a cellulosity, or even a 

 continuous parenchyma, and in which the greatest development of alimentary organs appears merely as ramifying canals with 

 external apertures ; 2nd, the Cavitary or Naematoid, in which the external covering encloses a cavity, containing a distinct 

 alimentary canal with mouth and vent. Instead of these designations, Owen prefers the names Sterclminthous for the former, and 

 Ccelehninthous for the latter Order. 



THE Sterelminthous Order have no distinct cavity for their alimentary ap- | 

 paratus, which consists of simple pores in their tegumentary covering, or 

 mere tubes continued from their mouths, without any other exit. They 

 exhibit very considerable difference in form, varying from the globular 

 shape of the Acephdocyst, to the lengthy, flat, tape-like Tcenia. The Tape- 

 worms are of considerable length, varying from three to ten feet, are flat, 

 and arc divided into segments, the hinder edge of one slightly overlapping 

 that which follows. The two genera infesting the human body are re- 

 markably distinguished from each other : the Tcenia solimn, which exists in 

 the English, Dutch, and Germans, has its fore part or neck narrow, and 

 merely marked by transverse rugse, but the greater part of the body consists 



Tape-worm. 



of oblong square segments : the head is small, wider than its length, has a 

 papilla, booklets, and four mouths. The Bothriocephalus lotus, which is 

 peculiar to the Russians and Swiss, is nearly of the same thickness through- 

 out, its segments are much wider than their length ; and its head, lengthy, 

 without booklets or mouth, has on each side a longitudinal cleft, or bothria, 

 by means of which their food is sucked up. 



The characteristics of the genus Tcenia are : Body often of very great 

 length, jointed, and tapering towards its anterior extremity ; head squarish, 

 with four mouthlets, and sometimes with a trunklet; in each joint one or 

 two ovarian apertures. 



The Coelelminthous Order include, among others, the Ascarides, one 

 species of which are of common occurrence in the human subject. They 

 are found not only in the intestines of man, and of the higher classes of 

 animals, but in those also of reptiles, and even of other worms. The sexes 

 are distinct, and the female is oviparous. The most important species, 

 because the only one which infects the human body, is Ascaris lurribricaides. 

 This species is not less than from six inches to nearly a foot in length, of a 

 whitish colour, shining, and somewhat hard and rigid in its structure. 



The generic characters of the Ascarides are : Body elongated, round, 

 often attenuated at the extremities ; three valves at the anterior extremity. 

 Mouth terminal, minute, covered by the valves. 



CLASS XIIL ACALEPHA. SEA-NETTLES. 



THESE Animals are mostly of transparent, gelatinous structure, and hence commonly known by the names of Sea-blubber or Jelly-fish ; 

 or, from the stinging sensation they impart when touched, Sea-nettles : this property was observed by the ancients, and hence also 

 the name <U-aX>;0cu, applied to them by Aristotle. They are furnished with locomotive organs, are capable of translating themselves 

 from place to place, and most of them are highly phosphorescent. 



ILLUSTRATIVE EXAMPLES. 



PLATE ACALEPHA. 

 Ehrenberg divides the Acalephs into three Orders : 



1. The Cterwphorous, or Crested Order, is characterised by longitudinal 

 rows of cilia or vibrating threads arranged in pairs, so as to form narrow 

 passages, which being connected with these locomotive organs are called 

 ambulacra. Their form is either a flattened spheroid, truncated at one 

 extremity like a deep cup, so as to form the aperture leading to the large 

 simple stomach, as in Beroe (Acaleph. Plate, fig. 1) ; or a much-compressed 

 ovoid, as in Mnemia, or a cylinder, with a pair of flatted wings, as in 

 Callianira (fig. 2), or a long flat ribbon, in the middle of which is the 

 stomach, as in the beautiful Cesium Veneris or Venus' girdle (fig. 3). 



2. The Sciaphorous Order is distinguished from the other Orders by the 

 umbrella-shape of the body. This peculiar shape varies considerably : 

 sometimes, as in Berenice (fig. 4), it is nearly flat, sometimes semiglobular, 

 as in Geryania (fig. 5), sometimes the lower edge is everted, like a bell, as 

 in Oceania, or contracted, as in Pelagia (fig. 6). The body is deepest in 

 the centre, and gradually thin towards the margin, where the convexity and 

 concavity unite. The margin is sometimes entire, as in Eudora and Ephrya, 

 or lobed as in Cyanea, or fringed with tentacles few in number as in 



Geryonia, or very numerous as in jEqwrea (fig. 7). The body of this 

 Order of Acalephs is a softish, jelly-like mass, loaded with water, trans- 

 parent, generally colourless, or varied with brilliant hues ; it is firmer about 

 the mouth and roots of the arms, and about the margin, tlian elsewhere. 

 When removed from the water, it soon dissolves almost entirely into a 

 saltish fluid, so that of an animal which had weighed fifty ounces, or even 

 twenty or thirty pounds, but a few grains remain. The motions of these 

 Acalephs are sometimes active, sometimes passive ; if desirous to move 

 forwards or upwards, they approximate the two halves of their margin 

 together, so that the convexity is bent still more like a bent bow, after 

 which the contraction suddenly ceases, and the animal is jerked onwards ; 

 having arrived near the surface, their umbrella remains outspread, and they 

 are borne along by the mere motion of the waves, till they choose to 

 descend, which is effected by contracting the whole disc and forming a ball, 

 after which they sink. In JEqvarea, the mouth which is circular is sur- 

 rounded with a simple rounded edge, which sometimes exhibits four or six 

 folds, or very slight notchings ; but in Aurelia (fig. 8), which has the mouth 

 cruciform, the edge is lengthened at each angle into a clasper, which is of 

 a somewhat trigonal form, rounded above, and hollowed slightly throughout 

 the whole length of its under surface or base. The many-mouthed or 



