26 INFUSORIA AND RHIZOPODA. <^§ 11, 12. 



pigment,® for the blue, violet and green pigments, seen in the eyes of in- 

 sects and Crustacea, show clearly that the red pigment is not essential to 

 the eye.* 



CHAPTER V . 



DIGESTIVE APPARATUS. 

 §11. 



Tlie Infusoria arc nourished, either by taking solid food into the interior 

 of their body, or by absorbing by its entire surface nutritive fluids which 

 occur in the media in which they live. 



This last mode is illustrated in the Astoma, which have no distinct oral 

 aperture or digestive apparatus. By the ingenious experiment tirst per- 

 formed by Gleichen,^^^ of feeding these animals with colored liquids, no trace 

 of these organs could be found. 



Ehrenberg, who also had observed that they did not eat, regarded their 

 internal vesicles as stomachal organs, which were in connection with the 

 mouth by tubes. The correctness of this opinion, however, has not been 

 verified. Indeed, the genus Opalina^'-' refutes it ; here the species are quite 

 large and visible to the naked eye, yet an oral aperture can be detected up- 

 on no part of their body, and never do they admit into its interior colored 

 jiarticles. Solid substances found in them cannot be regarded as food. 

 That fluids are here introduced by surface-imbibition is shown by Opalina 

 ranarum ; this animal is found in bile in the rectum of frogs, and assumes 

 a green color. When Opalina requiring only a certain quantity of 

 liquid are placed in water, they quickly absorb it, become greatly swollen, 

 and shortly after die. In such cases, the absorbed liquid is seen as clear, 

 vesicular globules under the surface, and these globules have been taken by 

 Ehreiiberg as stomachal vesicles (ventriculi), and by Dujardin as 



VACUOLAE. 



§ 12- 



Those Infusoria which are nourished by solid food have a mouth at a cer- 

 tain place, and an oesophagus traversing the parenchyma of the body. 

 Through this last the food is received, and is finally dissolved in the semi-liquid 

 parenchyma of the body, without passing through stomachal or intestinal cav- 

 ities. In many cases there is at the end of the body opposite the mouth an 

 ANUS, through which the refuse material 'is expelled. But, when this is 



"* " Die Infusionsthierchen," p. 492. - The genus Opalina was first established by 



1 Auserlesene luilcroskopische Eiitdeckungeu, Purkinjf. 6; Valentin. Many species are Ibuml 



1777, p. 51 ; also, Abhandluug iiber die Saaraen- in the rectum of frogs, and it is not rare to meet 



und Infusionsthierchen, 1778, p. 140. with them in the alimentary canal of Planarieae.f 



*Some recent researches of Thuret (Ann. d. So. fact Is a very interesting one in this connection. — 



Nat. 3rd ser. XIV. 1850) on the reproductive germs Ed. 



of Algae prove that these bodie' have red eye- t [ § 11, note 2.] According to Agassiz (Amer. 



like specks, resembling those seen in the Polygas- Jour. Sc. XIII. 1852, p. 425), Opalina is only u 



trica, but which disajipear when the Zoospores at- larval form of Distoma. — Ed. 

 tach themselves and germination proceeds. The 



