202 



LOWER INVERTEBRATES. 



crenullated edges ; the cups are soldered together in the median line ; a similar arrange- 

 ment, but on a much smaller scale, exists in Soleiiophorus, and indeed thei'e can be no 



doubt that both the genera alluded to belong to the 

 family of Bothi'yocephalidaj. 



Our herbivorous domestic animals are much infested 

 by tape-worms, the horse, sheep, goat, and cattle, each 

 have distinct species. The horse is especially subject to 

 (lieir attacks, and has three species peculiar to itself, 

 namely, Tanda plicata., T. rnamillana, and T. perfoliatu. 

 These vrorms sometimes occur in large numbers in a 

 single host ; Chabert counted ninety-one from one horse. 

 It is supposed that these species have free-swimming 

 aquatic larvae, which the horses swallow in drinking; 

 but of none of them is the history satisfactorily known. 



Thus we terminate our brief account of the parasitic 

 plathelminths. The subject is a repulsive one, but is full 

 of instruction to the thoughtful naturalist. To trace out 

 the life histories, so baffling to the student, has required 

 the greatest perseverance and acumen ; and our present 

 knowledge is a very remarkable monument to the patience 

 and skill of scientific naturalists. 



Class II.— EOTIFBRA. 



The IJotifera or wheel-animalcules are small creatures 

 found in marine and fresh waters, but most abundant in 

 stagnant pools, and often in places where water has stood 

 for a few weeks only. They equal a pin's head in size, 

 and are very transparent, so that an entire animal may 

 be forced to display its complicated anatomy at one view to the inquisitive micro- 

 scopist. They are all, except the sessile forms, agile and restless, and dart about 

 eagerly and rapidly, so that they are hard to follow with the eye ; but, fortunately, 

 they have a liking for occasional repose, and will sometimes keep delightfully still, 

 long enough for the keen observer to discover some 

 of the secrets of their organization and of their 

 physiological processes. 



One of the most familiar forms is the little 

 wheel-bearer. Rotifer vulgaris., which may be col- 

 lected during the warm season from almost every 

 ditch. The body of this animal, when fully ex- 

 tended, possesses greater length, in proportion to 

 its breadth, than most others of its class. The tail 

 commonly has three joints or segments which are 

 capable of being drawn one within the other. This 

 animalcule may be considered typical of its class. 

 There are no legs ; the anterior portion of the body 

 is furnished with a retractile lobed disc, of which the margin is covered with vibra,tile 

 cilia, while at the opposite end of the body is a cylindrical process forked at its ex- 



FlG. 186. — Duth'icrsia expalisa. 



Pig. 187. — Mastax of Euchlanis. 



