ZOOLOGY ANL) BOTANY, MICKOSGorY, KTC. 



433 



object to be exaniined is mounted may be inserted in this i^ap snid the 

 focusing handle rotated until it just closes on the slide. The illumioator 

 is now set at the correct focus for the particular thickness of the slide. 



As the gap is just above the level of the substage this small opera- 

 tion may easily be carried out while the dark ground illuminator is in 

 place on the microscope, or, if necessary, the substage can be swung out 

 for the purpose and then replaced. 



A Simple Method for Handling- Small Objects in Making 

 Microscopic Preparations.— Chas. W. Metz {The Anatomical Record, 

 21, lt)21). The following metliod of handling flies, especially Droso- 

 pkila and other small forms, has been worked out by the author and 

 proved satisfactory. 



It resembles the well-known method of wrapping the objects in 

 some flat, transparent membrane like Gryptobi'anclius epidermis, but 

 utiHzes the thin transparent bag-like skin which surrounds the abdomen 

 of the Drosophila (fruit-fly, vinegar-fly, banana-fly) pupa under the 



Pig. 5. 



PlC4. 6. 



chitinous pupa case — at about the middle of the pupal stage. This 

 skin is obtained intact by puncturing the pupa with a needle about a 

 third of the way back from the anterior end (end with the long 

 " horns "), then transferring to water and tearing it in two with dissect- 

 ing needles, after which the abdomen and the attached portion of the 

 thorax may easily be pulled or pressed from the pupa case and the 

 contents removed by gentle pressure with one needle while the apex of 

 the abdomen is held down with the point of another : there then 

 remains an oval, transparent bag with a constricted opening at the 

 anterior end representing the connexion between the abdomen and the 

 thorax. The small objects to be treated are passed through this orifice 

 into the pouch until the latter is nearly full and then the opening 

 closed l)y pressing or twisting the edges together with needles or 

 forceps and immersion in the fixative or alcohol. Olijects are usually 

 fixed, washed, and run up to f)!) p.c. alcohol before packing into the 

 pupa-skins. This avoids any long stay in the dissecting fluid during 



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