12 INTRODUCTION TO ZOOLOGY. 



or more species peculiar to itself. If so, the number of 

 species among the Entozoa must exceed that of all other 

 animals existing in the world. 



These singular beings differ widely in their structure. 

 Some, resembling delicate transparent membranes filled with 

 water (Fig. 5), appear more simple than any of the Infusoria; 



others are so complex, that, 

 in some respects, they seem 

 allied to animals of a much 

 higher rank in organization. 

 Many details pertaining to 

 their abode, their nutriment, 

 and their means of increase, 

 though interesting to the na- 

 turalist, and important to the 

 rig. 5. CYSTIC ENTOZOON. physician, would here be out 

 of place. But as the Entozoa 



constitute one class of the animal kingdom, and cannot, 

 therefore, be passed over in silence, a brief notice of some 

 of their peculiarities may be inserted. 



They are found in the stomach, in the intestines, in the 

 bronchial tubes, in the biliary ducts, and even in the humours 

 of the eye. The farmer is well acquainted with two kinds, 

 one of which exists in the brain and the other in the liver of 

 the sheep. One species, which infests the human body, is the 

 common Tape-worm (Tcenia solium, Fig. 6), which is occa- 

 sionally found several yards in length. Its head is furnished 

 with four suckers and two rows of recurved bristles, by means 

 of which it is enabled to fix itself securely to any spot it 

 selects. The most singular trait in the structure of the crea- 

 ture is the multitude of its joints, and the power which each 

 of these joints possesses of producing thousands of fertile ova. 

 When these ova come to maturity, the lower segment of its 

 body breaks off from the upper: the Tape-worm may, from 

 this peculiarity, be compared to trees or plants which fling cflf 

 their seeds when they come to maturity. When the lower 

 segment of the worm separates from the upper portion, the 



Fig. 5. a, Cysticcrcus cellulosce, magnified. b, the head still further enlarged. 



NOTE. It is this species which is found in the cellular tissue of the 

 Pig, and which, when abundant, gives to the flesh of the animal the 

 appearance which has been termed measles, or measly. Vide Dr. Bel- 

 lingham on Irish Entozoa, in Annals of Nat. History, 



