198 SECTION C. INVERTEBRATA. 



Rotifers cannot be killed off-hand by osmic acid or other agent, 

 without complete contraction, and it is therefore necessary to use a 

 narcotic, and the best for this purpose has been found to be a mixture 

 of cocain and methylated spirit made as follows : 



2 per cent, solution of hydrochlorate of cocain... 3 parts 



Methylated spirit i „ 



Water 6 „ 



The Rotifers must first of all be isolated, by picking them up 

 one by one if necessary, in perfectly clean water in a watch-glass ; 

 one or two drops (not more) of the narcotizing solution is then 

 added ; after 5 to 10 minutes a few more drops are added, and so 

 on until the animals move very slowly and, on trial, can be killed 

 fully extended. The killing and fixing agent is very weak {{ to 

 ^7o) osmic acid of which one drop only is added, and after one 

 minute the animals are washed by transferring them by means of a 

 very fine pipette into several changes of clean water, so as to re- 

 move all traces of the acid. Finally the Rotifers are transferred 

 into 2i 7o solution of formaldehyde (2h parts of the commercial 

 40 7o formalin and 37^ parts distilled water) in which fluid they 

 are also mounted on micro slides with hollow ground cavities. 

 The whole process is necessarily performed under a dissecting 

 microscope. 



For further particulars of details of manipulation and treatment 

 of some difficult species, I will refer you to two papers I have 

 published in the Journal of the Quekett Microscopical Chtb of July 

 1893 and March 1895. 



By this method I have so far made a collection of over 400 

 slides, containing about 260 different species of Rotifers, some 

 samples of which are exhibited under 18 microscopes in the 

 Zoological Laboratory, which will enable you to judge of their 

 merit. 



Since the publication of Hudson and Gosses' monograph in 

 1889 a large number of new species (355) of Rotifers has been 

 described ; many of these forms are merely synonyms and were 

 previously known, but had not been figured and described with 

 sufficient accuracy. It seems to me that collections of this kind 

 afford the best means of identifying doubtful species and preventing 

 the growing evil of giving new names to already known forms. 

 I would suggest that mounted specimens of all Rotifers that are 

 described as new should be deposited in some museum, say of 

 Cambridge, where they would be accessible to examination. 



