DIFFICULTIES AND OBJECTIONS 24 1 



thick canals, and referred to in a previous chapter. 

 Such additional peculiarities and specialties might be 

 multiplied to any extent from the numerous prepared 

 specimens now in our collections. 



One object which I have in view in thus minutely- 

 directing attention to these illustrations, is to show 

 the nature of the misapprehensions which may occur 

 in examining specimens of this kind, and at the 

 same time the certainty which may be attained 

 when proper precautions are taken. I may add 

 that such structures as those referred to are best 

 seen in extremely thin slices, and that the observer 

 must not expect that every specimen will exhibit 

 them equally well. It is only by preparing and 

 examining many specimens that the best results can 

 be obtained. It often happens that one specimen is 

 required to show well one part of the structures, 

 and a different one to show another ; and previous 

 to actual trial, it is not easy to say which portion 

 of the structures any particular fragment will show 

 most clearly. This renders it somewhat difficult to 

 supply one's friends with specimens. Really good 

 slices can be prepared only from the best material 

 and by skilled manipulators ; imperfect slices may 

 only mislead ; and rough specimens may not be 



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