94 INFUSORIA POLYGASTRICA. 



tinct ovary (Jig. 82, a). The body of this creature consists of a 

 great number of these segments, united together in a linear series 

 (Jig. 83) : the segments which immediately succeed to the head 

 (a) are very small, and so fragile that it is rarely this part of the 

 animal is procured in a perfect state; they gradually however 

 increase in size towards the middle of the body. Each segment 

 of the tape-worm may be regarded as a distinct animal, for it 

 possesses the means of reproducing itself; yet the alimentary 

 tubes are common to them all, those of each joint freely com- 

 municating with the nutritive canals of the adjoining segments. 

 The first joint of the Tse'nia, which may be called its head, differs 

 materially in structure from all the rest; it is in fact converted 

 into an apparatus by means of which the entire animal derives 

 its nourishment. This part, when highly magnified, is found to 

 be somewhat of a square shape; in the centre is seen -the mouth, 

 surrounded with a circle of minute spines, so disposed as to 

 secure its retention in a position for imbibing the chyle in which 

 it is immersed. Around this mouth are placed four suckers. 

 Tape-worms infest all classes of animals, and commonly inhabit 

 the small intestine. Their presence in the alimentary canal 

 generally causes debility and wasting of the body, and often 

 very serious disturbance. The species which attacks man, " the 

 solitary worm," is very difficult to get rid of. 



We also place in this division certain very singular animals, 

 which resemble a little bladder filled with water ; they grow in 

 different parts of the bodies of animals, and are called Hydatids. 

 They are the cause of considerable disturbance and serious dis- 

 eases. 



12. INFUSO'RIA POLYGAS'TRICA. These animalcules can only 

 be perceived by means of the microscope ; they are abundantly 

 developed in water containing the remains of organic bodies ; 



6 31 



Fig. 84. POLYAGASTRIC INFUSORIA. 



12. What are the characters of the polygastric infuso'ria ? 



