LESSON 29.] 



THE ORGANS OF NUTRITION. 



99 



glass, and all the organs described can be seen in the microscope, if 

 it remain quiet, with the utmost distinctness ; it will be apparent 

 that the alimentary canal, and all the organic structures, have made 

 a great advance from the simple sacculated condition, and only one 

 aperture of the Vorticella, and its allies. 



494. These animals are remarkable for their tenacity of life. 

 As early as the year 1701, Leeuwenhoek had been examining some 

 specimens of Rotifer vulgaris, and left FlG 169 



the water in which they were con- 

 tained to evaporate. Two days after- 

 ward, having added some rain water, 

 previously boiled, within half an hour 

 he saw a hundred of the Rotifera re- 

 vived, and moving about ! 



A similar experiment was made, 

 with the same results, keeping the 

 animals dried up for a period of five 

 months ; and this has been repeated, 

 and confirmed by many subsequent 

 authorities, the time being extended 

 to three years. 



ENTOZOA. 



495. The Entozoa are parasitic 

 internal, or intestinal worms ; of 

 these, every known animal has its 

 own peculiar species, and usually 

 more than one ; in man, no less than 

 eighteen different species have been 

 detected, occupying the various cavi. 

 ties and tissues of the body. 



496. Excluded from the influence 



of light, they are almost uniformly white in color ; deprived of air 

 they do not possess organs of respiration ; they 

 are, in short, little (if any thing) but sacs for 

 the imbibition of nutriment. 



497. The Acephdlocyst (Fig. 170) consists 

 of a globular or oval vescicle filled with fluid ; 

 sometimes suspended freely in the fluid of a cyst 

 of the surrounding condensed cellular tissue, de- 

 veloping smaller acephalocysts, which are discharged from the outer 

 or the inner surface of the parent cyst. 



Notommata clavulata. 

 &, 6. Longitudinal muscles, which 

 shorten the "body. 



c, c. Transverse muscles, which dimii 



nish the breadth of the body. 



d, d. Ganglions (nerve knots) of the 



neck. 



e. Cervical ganglion. 

 / Pharynx, containing the jaws. 

 g. Alimentary canal, terminating 



h. a Cloacal outlet. 

 i. Glands, either salivary or liver. 

 Jc. Eeproductive tubuli. 

 m. Forcipated instruments for pre- 

 hension. 



FIG. 170. 



The Acephalocyst. 



