Mites 



GUM MOUNTS 



45 



tomarily collected. The only difficulty in 

 using this equipment is in preventing the 

 heat from getting too great. Some people 

 use so large a lamp above, and so high a 

 temperature around the edges, that many 

 small arthropods are killed before they 

 have time to fall into the trap which has 

 been laid for them. The outer water for 

 most uses should be at a temperature of 

 30° to 40°C., while the lamp above should 

 under no circumstances raise surface tem- 

 perature of the material above 60°C. 

 These temperatures are for a moderately 

 dry moss sample, and may be considerably 

 exceeded when one is dealing with a drj^ 

 material such as straw. Wet moss of the 

 sphagnum type, however, requires lower 

 temperatures. 



Assuming that permanent mounts are 

 to be made, for record purposes, of all the 

 small invertebrates which may be found 

 in a moss sample, it is necessary to make 

 adequate preparations to receive them 

 while the moss is being treated. Two kinds 

 of gum mountants are desirable: a high- 

 refractive-index medium like Berlese, for 

 the very heavy-walled forms such as the 

 Oribatid mites and the Pseudoscorpion- 

 ides; and a low-refractive-index mountant, 

 like Gray and Wess, for the thinner-walled 

 forms such as the Tyroglyphid and Gam- 

 assid mites. This last medium is also 

 suitable for Thysanura and for CoUem- 

 boUa. Thick-walled beetles and fleas, if 

 they are to be made into microscope 

 slides, had better be treated as described 

 in Chapter 6, and should be accumulated 

 for this purpose in a tube of 95% alcohol. 

 Sphagnum moss is also likely to yield a 

 number of crustaceans, particularly Cla- 

 docera and Ostracoda. These are better 

 mounted in glycerol jelly, in the manner 

 described in the next chapter, and should 

 be transferred as soon as they are found to 

 30% alcohol where they will die with their 

 appendages extended. They should not, 

 however, be permitted to remain in this 



weak alcohol for longer than is necessary 

 to kill them, but should then be trans- 

 ferred to 95% alcohol. A considerable 

 number of nematode worms are likely to 

 turn up and should be treated as de- 

 scribed in the last chapter, while a tube of 

 some fixative should be provided to re- 

 ceive any small annelids which may be 

 found in the gathering, and which must be 

 fixed, stained, and mounted at once. A 

 brush will also be required, a supply of 

 clean 3" X 1" glass slides, and a numljer 

 of covershps. 



All being ready, and observation show- 

 ing that no further forms are falling 

 through the Berlese funnel, the collecting 

 tube beneath it is now inspected to see 

 roughly what one has gathered. If there 

 are a considerable number of Gamassid 

 mites or active insects, it is necessary 

 gently to open a portion of the tube by 

 pushing away the modelhng clay with the 

 thumb and to let a minute drop of ether 

 run down inside. When this has been done 

 the tube is removed and the contents 

 tipped out into a petri dish or similar con- 

 tainer and the catch sorted. 



A mite, or similar form, which is to be 

 mounted, is then picked up on the tip of a 

 brush and transferred to a drop of the 

 mountant. As little water as possible 

 should be transferred with it and the mite 

 should be pushed under the surface of the 

 gum with the point of a needle. The mount 

 is then inspected under the low part of the 

 microscope and, if any large quantity of 

 air has been carried in with the mite, the 

 bubbles are released with the aid of a fine 

 needle and allowed to come to the surface 

 before the covershp is laid gently into 

 place. The drop of gum should be of a 

 considerable size and no endeavor should 

 be made to press the coverslip down. If a 

 reasonably thick layer of mountant is left 

 almost any small arthropod will spread its 

 legs like a textbook diagram before dying 

 and will remain in this form indefinitely. 



