THE MICROSCOPICAL PREPARATION OF INSECTS 225 



carbol-xylol is useful, however, as an intermediary, and also 

 ensures perfect dehydration. 



These preparations are interesting, the internal organs 

 being well seen in situ. The larva may also be killed by 

 being dropped into hot water (not boiling, but "newly off 

 the boil") and kept hot for ten minutes to fix the tissues. 

 The specimen is then transferred to 30 per cent, alcohol 

 and taken up by gradations of 5 per cent, to absolute alcohol 

 a more tedious process. 



I have sometimes been asked why I do not more often 

 use glycerine jelly as a medium for mounting insects, 

 convenient and quick of application as it seems. In the first 

 place few insects are transparent enough to be mounted in 

 it with a view to examination by transmitted light, and it 

 does not add transparency to them to the extent that 

 mounting in balsam does. Another objection is that it is 

 apt to crush delicate structures, antennae, etc. There are 

 cases, however, when insects treated by KOH become 

 rather too transparent in balsam, and yet are sufficiently 

 well shown in glycerine jelly, because of its lower refractive 

 index. When this is the case the trouble of staining may 

 thus be saved. I give the following method for preparing 

 Tricliodcctes latus, as a sample of a case where glycerine 

 jelly was preferable to balsam as a mounting medium. The 

 difficulty with Trichodectes is to display the front legs, which 

 are small and have an obstinate tendency to curve inwards 

 and disappear altogether under the broad head, a tendency 

 which is increased by treatment with alcohol. In pulling 

 them out one is very apt to break them. With the 

 glycerine jelly method, alcohol is avoided altogether, and the 

 legs retaining their flexibility throughout the process, can 

 eventually be "coaxed" into position without any manipula- 

 tion. The material was preserved in formalin : 



After washing out the formalin, boil in KOH twelve minutes. 



Wash well in distilled water. 



Treat with glacial acetic acid about six hours. 



Wash in several changes of water. 



Leave in water overnight. 



Mount in glycerine jelly, using plenty of it. 



