COMPARATIVE ANATOMY. 



241 



COMPARATIVE ANATOMY. VII. 



HKLMINTHOZOA. 



Au, the animala of which we have hitherto treated have been 



iuliubitanta of the water. Those which form the subject of the 



present lesson have a very strange habitat. They, for the most 



part, take up their abode in the interior of other animala, being 



found in tho alimentary canal when they have become completely 



developed, but occupying all the several soft structures of the 



of the higher animals when in an immature condition. 



.. :-it'T.s have been disposed to treat of thorn not as a 



i or class in the animal kingdom, but as a peculiar 



fauna or assemblage of animals occupying a peculiar locality. 



Just us we inlu'lit describe the animals of Europe, dividing that 



continent into natural districts, and stating what kinds of 



animals are confined to the Alpine region, what kinds are 



enigma*. Those who believe that *nimii.l were introduced to 

 the globe, created, or derived from one another in the order of 

 their development or position in the scale of Nature the 

 simplest animals coming first in time are at a loss to account 

 for the appearance of these animals. Standing next above the 

 Eohinodermata, they should precede all the higher grades of 

 animals, and yet their very existence and history implies the 

 presence of animals of a higher grade, who act towards them as 

 hosts. Again, these animals offer strange exceptions to the 

 harmony of Nature. It is true that all animated Nature u a 

 battle-field, in which species carry on their unrelenting hostili- 

 ties towards one another ; but this very strife results in an 

 admirable harmony, there being a place for each species, while 

 each is held in check by the others. The sickly and wretched 

 make way for the robust, and strong, and joyous. On the other 

 hand, that an otherwise strong and robust .r,imftl should 



I. HEAD AND FOREPART OF THE BODY or TJENIA SOLIUM, SHOWING THE HOOKS AND SUCKERS. II. ONE JOINT or THE SAME TAKEN FROM VEAR 



THE TAIL-END OF THE ANIMAL, SHOWING THE CENTRAL REPRODUCTIVE ORGANS WITH THEIR DUCTS LEADING TO THE SIDE, AND ALSO THE 

 WATER-VASCULAR SYSTEM. III. HEAD OF THE LARVA OF TXNIA SOLIUM (CYSTICERCU8) PROJECTING INTO THE BLADDER-LIKE CYST. IV. 

 DlSTOKA CONJUNCTUM. V. LlVEIC FLUKE (FASCIOLA HEPATICUM), SHOWING THE BRANCHING ALIMENTARY CANAL AND THE TWO SUCKERS. 



VI. OXYURIS VERMICULARIS (MALE). 



Kefs, to Nos. in Figs. IV. 1, double alimentary canal ; 2, mouth sucker ; 3, ventral sucker ; 4, water-vascular system ; 5, female organ ; 6, 

 glands which form the egg-yolk ; 7, male organs. 



partial to the plains, etc. : so would these authors consider the 

 bodies of the higher animals as the continents in which these 

 strange creatures have their range ; and state how some are 

 prone to take up their abode in the liver, some are lodged in the 

 brain, and others find their home in the muscles. This, however, 

 is certainly not a scientific view of the subject, and the facts of 

 the cose do not compel us to adopt it. For though there is 

 doubtless much diversity in the structure of these animals, and 

 they show relationships to two if not more classes, yet those 

 included under the class we name Helminthozoa are so far dis- 

 tinguished as to make up a definite class, which, however, does 

 not quite run parallel with the class Entozoa, inasmuch as it 

 includes some animals which never take up their abode in the 

 interior of others. Tho class Entozoa was never a good 

 designation, as many of these animals that are the most typical 

 of their class, as intestinal worms, pass some of their stages of 

 existence in water, etc., outside the bodies of animals. 



These creatures offer to the speculative faculties many 

 42 N.E. 



become the prey of internal parasites, which do not strike it 

 down and put it at once out of its misery, but cause emaciation 

 and slow and painful death, seems strange, when we consider 

 that the whole of creation was fashioned to one design by a 

 supreme and benevolent Being. These remarks are, of course, 

 only offered to show how impossible it is for us to understand or 

 account for all the works of the Infinite. 



One of the best known and most typical forms of the lowest 

 sub-class of Helminthozoa , ia the common tapeworm, called Taenia 

 solium. The name Taenia means a band, and is given because of 

 the long, flat, strap-shaped character of the animal's body. The 

 specific or trivial name, solium, meaning solitary, was given 

 because it was at first imagined that only one of these animals 

 were ever found in one person at once. This, however, has been 

 proved to be a mistake. 



This disgusting creature is found in the alimentary canal of 

 man. It is often many feet or even yards in length. Its head ia 

 armed with two kinds of organs for effecting its adhesion to the 



