458 SOME ZOOLOGICAL METHODS. 



best done by gently tapping the cover-glass (which may be 

 supported on wax feet). This gives far better results than 

 teasing with needles. A camel-hair pencil also sometimes 

 renders good service. 



854. Siphonophora. This group contains some of the most 

 difficult forms to preserve that are to be found in tho whole 

 range of the animal kingdom. You have not only to deal 

 with the very great contractility of the zooids, but with the 

 tendency to general disarticulation of the swimming- bells and 

 prehensile polyps. 



The cupric sulphate method of BEDOT, 44, is practised 

 as follows : Bedot directs that a large quantity of 15 to 20 

 per cent, solution of the salt be suddenly added to the sea 

 water containing the animals. As soon as they are fixed 

 (which happens in a few minutes) a few drops of nitric acid 

 are to be added and mixed in (this is in order to prevent the 

 formation of precipitates), and the whole is left for four to 

 five hours. The specimens are then to be hardened before 

 bringing them into alcohol. Bedot recommends that this be 

 done with solution of Flemming. The strong solution is the 

 one that should be taken, and it should be added to the solution 

 of sulphate containing the Siphonophore, about two volumes 

 of it being taken for one of the sulphate solution. The whole 

 should be left for at least twenty-four hours. After harden- 

 ing in the mixture a few drops of 25 per cent, alcohol should 

 be added to the fluid with a pipette, being dropped in as far 

 as possible from the colony, which should be disturbed as 

 little as possible ; and further alcohol, of gradually increasing 

 strength, should be added so gradually that the strength of 

 70 per cent, be not attained under fifteen days at least. 

 Ninety per cent, alcohol should be used for definite pre- 

 servation. 



I have tested this method. I do not find that the his- 

 tological preservation is superior to that obtained by means 

 of the usual processes ; but the method is certainly a valuable 

 one in so far as it enables one to preserve specimens with all 

 their swimming -bells and polyps in situ, a result which is not 

 obtained by means of the usual methods. 



The cupric and zinc sulphate mixture of FRIEDLANDER has 

 been given, 44. 



