107 

 ORGANS OF NUTRITION. 



The act of nutrition and its organs are objects 

 of difficult observation in this series of animalcules, 

 on account of the impossibility of using the means 

 employed by Mr. Ehrenberg in the investigation of 

 the true Infusoria, because the creatures, mentioned 

 in this inquiry, do not admit colouring substances. 

 Analogy alone can assist us, and even very weakly, 

 in these researches. 



In the Surirellae and Naviculae I could not dis- 

 cover any tnbe running parallel to the body. 



We see, however, in the Surirella Venus a skin 

 separating itself from one of the points of the coat, 

 in which skin d. fig. 4.) there is an incision , lea- 

 ding to the content (V). By means of this overture, 

 the animalcule throws out entirely the content; but 

 I never could distinguish upon the coat any opening 

 nor fissure. 



The Naviculae, according to my classification, 

 include the species of the most ancient genera of 

 Frustuliae and Naviculae ; which, next to the pedal 

 surfaces (fig. 4. 8. e.) , found in the axe of the 

 body, are supplied with two openings (d. d.) leading 

 to two empty tubes (f. f.) passing through the whole 

 animal, and, on both opposite extremities, terminated 

 also by two holes, near the smooth pedal surface. 



In the Navicula costata (fig. 10.} these two ope- 

 nings arc found under the flat pedal surface, and 



