58 



NATURAL HISTORY. 



[Lesson XIV 



LESSON XIV. 



have the remaining four classes of the Radiated animals to examine, viz. 2. The 



ENTOZOA, or intestinal worms. 3. The 

 ACALEPHJE, or sea-nettles. 4. The POLYPI, 

 or animals with many feet. 5. The IN- 

 FUSORIA, or animalcules. The Entozoa are 

 remarkable for being the inhabitants of the 

 internalparts of other animals, especially the 

 Vertebrata, but the other animals are scarcely 

 ever affected with them. Some of them at- 

 tain a large size, especially such as the taeuia, 

 which are often twenty feet long, and some- 

 times more than a hundred feet. The Aculepha 

 have been divided into the simple and the 

 hydrostatic, and include all those animals. 

 The Polypi are capable of producing new 

 individuals, both by putting forth a kind of 

 bud and by eggs, .which are left to the 

 mercy of the waters. The Infusoria are 

 little known, although Ehrenberg, Pritchard, 

 Owen, Grant, and others have written 

 upon them, yet much remains to be dis- 

 covered, as regards their organization, and still more in classifying them. 



QUESTIONS. 



178. T. For what are the Entozoa re- 

 markable ? 



P. Inhabiting the interior of other 

 animals, where they can only exist. 



179. T. Is there anything peculiar in 

 their organization ? 



P. Yes ; they have no breathing ap- 

 paratus, which shows that the nutriment 

 they receive is aerated by animals upon 

 which they are parasitic. 



180. 7 1 . Are the species of the Entozoa 

 numerous ? 



P. Yes ; and they are divided into two 

 distinct orders the Nematuidea, or cavi- 

 tied entozoa, and the Entozoa Parenctn/v/afa, 

 which have the viscera obscure, the body 

 being filled with a pulpy matter. 



181. T. Give me some examples of the 

 order Nematoidea, and their peculiarities. 



P. The order Nematoidea comprises 

 several genera which are remarkable for 

 having no circulation that we can discover, 

 and a simple nervous system which is only 

 seen in some species, consisting of two 

 cords extending from a ring round the 

 mouth. The thread-worms ;md ascarides 

 are familiar examples of this order. 



182. T. Give me some examples of the 

 second order, and state something about it. 



P. The order Pareiichymata contains 

 four families, and is remarkable for an 

 absence of an alimentary apparatus, and 

 no visible signs of a nervous system. The 

 fluke found in the livers of sheep ; the 

 tape-worm (see Fig. 26'*) ; and hydatids, 

 are all examples of this order. 



183. T. What is supposed to be the 

 use of the Entozoa ? 



* Fig. 26. The Taenia tolinm, or solitary worm, exhibiting the alternating pores, head with suckers, 

 and the narrow anterior, or neck part. 



