INFUSORIAL ANIMALCULES. 67 



nated by a digestive sac. In the families Vorticellina and 

 Ophrydina, the two ends of the alimentary canal approach 

 each other, and form but one external opening. In the 

 Enchelia and Colepina, the orifices are at the opposite 

 extremities of the body ; in Trachelina, Ophryocercina, and 

 Aspidiscina, they terminate obliquely with respect to each 

 other ; and the remaining families are distinguished from 

 the preceding by both openings being situated on the 

 under side of the animalcule. 



Section XXVII. — Geographical Distribution of Poly- 

 gastric Infusoria. 



This is the most universal of the Animal Kingdom. It 

 is known to extend over the whole of Europe, the 

 north of Africa, the west and north of Asia, and species 

 have also been observed in America. The largest and 

 most generally-distributed family of this class is the 

 Bacillaria, its species equalling one-fourth of the whole. 



Fossil states of this curious family are known in 

 Europe, Africa, the Isle of Bourbon, the Isle of Lucan, 

 amongst the Philij^pines, and America. These remains 

 enter into some of the new sand-stone formations ; also 

 into the layers of flints of the secondary formations, cer- 

 tain porphyritic structures, &c. 



Some objections have been made by a few eminent 

 naturalists to certain families of Dr. E.'s Infusoria. The 

 most important of these I have inserted under their 

 several heads in Part II. Those of Dr. Meyen, which are 

 unknown to the English reader, contain many important 

 remarks, and are worthy of special notice. 



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