BOOK SIXTH. 



TURBELLAHIA 



CLASSIFICATION. 



§120. 



The Turbellaria receive their name from the ciliated epithelium, which 

 covers their whole body. Their flattened, or cylindrical, non-articulated 

 body, is formed of a loose parenchyma, in which lie hid the viscera. The 

 nervous system appears very little developed, and when visible, consists only 

 of a cervical ganglion, from which there never extends a ventral cord. 

 The multiramose intestinal canal is always without an anus. The genital 

 organs are either very much developed, or entirely absent.*^* In the first 

 case, these animals are always hermaphrodites, and have copulatory organs. 



The Turbellaria have been shifted from one zoological system to another, 

 but their organization has sufficient peculiarities to entitle them to a special 

 class by themselves. 



Ehrenberg was the first to found the group Turbellaria ; but he has in- 

 cluded therein many difierent animals ; and we are, therefore, indebted to 

 Orsted, for a late revision of this group. 



ORDER I. RHABDOCOELL 



The alimentary canal is simple and cylindrical ; the oesophagus, non- 

 protractile ; locomotion, mostly natatory. 



Genera : Vortex, Derostomum, Gyratrix, Strongylostomum, Mesostomum, 

 TypJdoplana, Macrostomuvi, Microstomum. 



ORDER 11. DENDROCOELL 



Intestinal canal dendritically ramified ; oesophagus completely protrac- 

 tile ; locomotion reptatory. 



1 I cannot here omit the question, if these small era, and if they are not rather the larvae of other 

 sexless Turbellaria, as for example, Derostomum, inferior animals, 

 and Microstom.um, really constitute distinct gen- 



