262 . MICROSCOPY FOR BEGINNERS. 



their color through the skin. In some these dark spots 

 become large, occupying much of the upper surface, and 

 so arranged and shaped that they leave between them 

 in the middle line of the body a Y-shaped space which 

 may be white, yellow, or other color. These spots are 

 called cosca or the ccecal markings, the word being the 

 plural of ccecum, meaning a certain part of the intestinal 

 canal. They are useful to the student in identifying 

 the species. 



The lower or ventral surface is the most important 

 part to the observer who desires to ascertain the name 

 of his specimen, or to the student who wishes to make 

 a more serious study of the animals, for on this surface 

 are the parts most used by the naturalist in classifying 

 the mites. The beginner must therefore seek to have 

 the little creature arranged on its back before it is 

 placed under the microscope, so that the ventral surface 

 shall be presented to the objective. This is sometimes 

 a difficult operation to accomplish without injuring the 

 delicate body. The writer has used for the purpose a 

 little home-made contrivance that answers well and can 

 be made by any one. A hole about half an inch in di- 

 ameter is drilled through a glass slip, and into one side 

 is cemented with shellac a thin glass circular cover a 

 little smaller than the hole, so that the thin cover may 

 not be flush with the surface of the slip. It is not 

 very difficult to grind a hole through a thin glass slip 

 if the file or other grinding tool is kept wet with tur- 

 pentine. The aperture may not be a perfect circle; it 



