360 COLLECTING, REARING [CH. 



either set or pinned with folded wings, in a special box with their exuviae 

 alongside them. 



Biological Methods. 



Chitiu-Preparations. Cut off the selected organ or part, and place it in 

 a strong solution of caustic potash for 24 hours or longer [or it may be boiled 

 in the same solution for from a minute or two to half-an-hour, according 

 to its nature]. Remove to physiological salt solution, and clean off all muscles, 

 etc. left on. Wash in distilled water. Transfer to 70 per cent, alcohol, 

 with at least one change. Run up through 90 per cent, to absolute alcohol, 

 thence to clove oil. The preparation may be conveniently examined in this 

 medium, and useless parts cut away. Mount in the usual manner with Canada 

 Balsam. For staining chitin-preparations I find a solution of Orange G in 

 water (24 hours or longer) gives the best results. Most chitin-preparations 

 from Odonata do not, however, require any staining. 



Cleared Larvae. Beautiful preparations of whole larvae, as well as of the 

 head, thorax, abdomen, branchial basket or caudal gills separately, may 

 be made as follows : Fix the larva (alive) in Carls' Fixative (see below) ; wash 

 out in 70 per cent, alcohol with several changes extending over 24 hours or 

 more; pass to 90 per cent, alcohol (6 hours), absolute alcohol (6 hours), 

 absolute alcohol + cedar oil, equal parts (24 hours), and finally into cedar oil. 

 Leave in cedar oil for a week or more (the longer the better). The whole 

 larva will gradually become of a glassy transparency, until all the internal 

 organs can be made out with great clearness. Keep the specimen always 

 in cedar oil in a tube. The opened branchial basket, or the caudal gills, 

 may be mounted in Canada Balsam within a raised ring. 



Stained Whole-Mounts. This method may be used for studying the 

 embryo, whole specimens of young larvae, various appendages (legs, caudal 

 gills) and portions of internal organs. Fix as above, and wash well in 70 per 

 cent, alcohol. Pass to 50 per cent, alcohol, thence to a solution of Grenacher's 

 Borax Carmine in 35 per cent, alcohol. Leave in stain until thoroughly 

 penetrated (24 hours to a week). Differentiate in 70 per cent, alcohol with 

 0-5 per cent, nitric acid added. Dehydrate, clear and mount in the usual 

 manner. 



Sections. Out of many methods which may be employed for this purpose, 

 I shall only give in detail the two which I find to be most suitable for the 

 Odonata in general. The processes are as follows: 



A. Single Embedding: 



1. Fix the animal, or part selected, in Carls' Fixative 1 ; formula: absolute 

 alcohol 15 parts, concentrated formol 6 parts, glacial acetic acid 2 parts, and 

 distilled water 30 parts. For whole larvae, make a small slit for penetration 

 of the mid-gut region (see above). Do not prolong fixation beyond 24 hours, 

 as the fixative will then have a "swelling" action on the cell-layers. 



1 Used by Carls and Kurt-Bedau for studying the compound eyes of insects. 



