24 



LECTURE II. 



cavities {^fig- 13. 6.) in the interior of the animal. In some species 

 these cavities have been so shown to be very numerous; and if, with 

 Ehrenberg, we call them stomachs, they afford a very interesting ex- 

 ample, in these early forms of animal life, of the irrelative repetition 

 of this most essential and characteristic organ of the animal. 

 Ehrenberg has described and figured certain definite arrangements of 

 these digestive cavities, as well as of the alimentary canal, to which 

 he states that they are appended. In the Monads, and many other 

 of the more minute species of the Polygastria, he affirms the stomachs 

 to arise by separate tubular pedicles from a common mouth, as shown 

 \njig. 11., copied from his great work. Such species have no intes- 

 tine, no anus, and are said to be anenterous. In others, he believes 

 the so-called stomachs to be appended to an alimentary canal {Poly- 

 gastria enterodela Ehr.) : which canal may be bent into a loop, and 

 describe a circle, with the anus opening near the mouth, as in Vor- 

 ticella {Jig. 12.) ; or it may pass in a straight line through the axis 

 of the body, as in Enchelis ; or form several flexuous curves in its 

 passage from the mouth to the opposite extremity of the body, as in 

 Leucophrys (Jig, 13.). But sometimes, as in the Kolpoda, neither 

 the mouth nor anus is terminal in position. 



Vorticella. 



It has been objected to this interpretation given by Ehrenberg of 

 the nature of the vacuolar which receive and assimilate the nutrient 

 molecules, that certain species, as the Enchelis pupa, will swallow 

 another animacule nearly equal to itself in bulk, and thereby undergo 

 a total change in the form of its body ; but this may only imply great 

 dilatability of the oesophagus or common canal, such as we observe in 

 the boa constrictor, which becomes in like manner deformed after 



