256 PROCEEDINGS OF THE ACADEMY OF [1898. 



taken will prove to have the reproductive organs fully developed. 

 Autumn and late summer are a somewhat less favorable time, be- 

 cause the young of the year have then attained the full growth of 

 the species, while upon opening them the genitalia are found un- 

 developed. Still, autumn specimens should be collected. Always 

 date each " catch " and keep it separate. 22 



The best preservative for slugs (and other land mollusks) is alco- 

 hol. Of other preservatives, formalin (formaldehyde) is perhaps the 

 best ; but it is, on the whole, a very unsatisfactory substitute, ren- 

 dering the tissues tough and slippery, difficult to dissect, and gener- 

 ally destroying calcareous organs in time. Formalin specimens are, 

 moreover, inferior to alcoholic for histological study. Upon the 

 whole, then, formalin should only be used as a permanent preserva- 

 tive for large slugs, if at all, and then in a three or four p. c. solu- 

 tion. It should be added, however, that when travelling with limited 

 means of conveyance, it is often convenient to use formalin on ac- 

 count of the economy of carrying it in the commercial strength, to 

 be diluted as occasion arises. Never crowd snails in formalin ; the 

 bulk of the solution should exceed that of the snails six or eight 

 times. 



After collecting slugs they should be drowned by placing in a 

 vessel of water with a lid laid on (not a cork pushed in) to exclude 

 air. Generally twelve hours is a sufficient time, but this depends 

 upon the slugs and the temperature. In hot weather less time is 

 required. Test them by taking one out, touching it with alcohol, 

 and if no retraction takes place they are ready to be transferred to 

 25% alcohol; 23 leave in this about twelve hours, then transfer to 

 50%, and after twenty-four hours or more to about 75%, in which 

 they may be permanently kept. 



If formalin is used, the slugs may be placed in the 3 or 4% solu- 

 tion when drowned, and changed to fresh solution after a few days, 

 the first being thrown away. Formalin specimens may at any time 

 be transferred to alcohol, or it may be used with a small percent, of 

 alcohol. 



22 Of course, for economy of space and alcohol, all the lots of one species 

 may be kept in one jar, each in a separate vial or piece of cheesecloth. 



23 Of course, in field work the exact proportion is not vital. In general, it 

 is best to use a mixture of three parts of water to one of alcohol at first, then 

 a half and half mixture, and then the permanent strength. The first and 

 second mixtures may be kept and used repeatedly, occasionally adding a 

 little alcohol to keep up the strength. 



