Branch Trochelminthes 33 



between them. Distinguish if you can the gullet leading 

 from the mouth, and lined with cilia. The so-called 

 teeth are visible at the inner end of the gullet ; behind 

 the teeth lie the stomach and intestine ; the latter ends 

 in an opening on the under side of the lorica near its 

 posterior border. 

 IX. — Make a good-sized drawing of the Rotifer. 



THE CLASSIFICATION OP THE ROTIFERS AND THEIR ALLIES 



Early in the history of zoological science the Rotifers 

 were classified with the Infusoria. But as soon as it was 

 seen that they were multicellular animals, it was necessary 

 to remove them from the branch Protozoa and to find for 

 them another resting-place in the system of classification. 

 No place seemed more fitting than the branch Vermes, 

 which was formerly made to include the worms and various 

 related creatures. It has long been recognized, however, 

 that the Vermes was too heterogeneous a collection to sat- 

 isfy the requirements of our knowledge, so that the latest 

 authorities have divided it into several groups, each with 

 the rank of a branch or phylum. The Rotifers, and two 

 other less abundant classes of minute animals somewhat 

 resembling the Rotifers, have been united to form the phy- 

 lum Trochelminthes. The young of these creatures exist 

 in the form of a trochosphere, which becomes modified dur- 

 ing the development of the animal. The class Rotifera is 

 much the most important one in this phylum. 



Four other groups have been separated from the Vermes 

 and raised to the rank of independent phyla. One of these, 

 the Annulata, is considerably higher than the rest and is 

 discussed later in this book in connection with the earth- 

 worm. 



