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ONYX AND DIPELTIS : 



NEW NEMATODE GENERA, WITH A NOTE ON DORYLAIMU3. 



By N. A. Cobb. 



I. 



Fixation and Preservation of Cojupressed Objects. 



Many sub-microscopic objects require to be compressed in order 

 to give the best results at the final microscopical examination, 

 and it is well known that compression cannot be accomplished 

 conveniently (if at all) after hardening. 



To illustrate by an example: the sub-cylindrical larva? of 

 dipterous insects if examined fresh are best seen in a compressorium, 

 but much histological detail is thus seen with difficulty, or escapes 

 observation altogether. If, however, it were possible to fix, stain 

 and mount the larva while compressed, a distinct advantage would 

 be gained. To describe a simple way of doing this is the object of 

 these preliminary lines. 



The object, say a dipterous larva or a rotifer or a tardigrade or 

 nematode, is compressed between two small coverglasses of the 

 same size. The amount of compression must be regulated by 

 means of two hairs, or better by two pieces of spun glass, placed 

 parallel to each other between the coverglasses. It will be found 

 that hairs from the head, eyebrows, and backs of the hands are of 

 different diameters, and a preliminary experiment will indicate 

 which it is best to use. Having laid the animal, together with 

 two hairs or bits of spun glass, on one of the covers in a drop of 

 water which is too small to entirely fill the space between the covers 

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