596 IN VERTEBRA TES 



the chitin puts for twelve to thirty-six hours into 3 per cent, 

 solution of sublimate with 5 per cent, of nitric acid. 



Nettovitch {Arh. z. Inst. Wien, xiii, 1900, p. 3) fixes Argulus 

 with liquid of Tellyesniczky, § 57, warmed to 50° C. 



For Fischel's intra-vitam staining of Cladocera with alizarin, 

 etc., see last ed. 



1182. Insecta, etc. The microtomy of the Arthropoda is 

 always tiresome, but usually very difficult in the case of the 

 insects. The development of a very intractable type of chitin 

 makes the sectioning of the larval, pupal or adult stages a difficult 

 business, and the embryonic stages are almost invariably provided 

 with masses of hard yolk. 



In fixation, mixtures containing nitric acid are indicated, 

 in imbedding celloidin, or the carbon bisulphide paraffin wax 

 methods are the best, and in sectioning the sliding microtome, 

 in which the knife acts with a slicing motion, is absolutely 

 necessary. 



Many years ago, we were shown a method for dealing with insect 

 material by Professor Sir Edward B. Poulton. This consisted neither 

 of special fixing nor imbedding methods, nor of the use of special 

 microtomes : the object imbedded in wax, say, a hard egg, was exposed 

 carefully on the side on which lay the yolk, and the latter was scooped 

 out with a suitably fine instrument, under the dissecting microscope. 

 Alternatively, the chitinous exo-skeleton of a hard ant or beetle was 

 picked off with needles, and the object re-imbedded. It is wonderful 

 what can be done by this method, but of course it is not applicable to 

 every object and does not get rid of internal chitin. Great help may 

 be got by killing beetles and such insects just after emergence before 

 the chitin has properly hardened. 



We have sectioned many types of insect eggs, and always 

 after imbedding merely in hard wax, using the celloidin paint 

 method, and a very sharp knife on a sliding microtome. Even 

 moth eggs can be sectioned successfully thus. 



In all cases every egg, before imbedding, and preferably while 

 in 70 per cent, alcohol, should be pricked with a very sharp and 

 very fine needle. This facilitates the penetration of the various 

 reagents, and shortens time of imbedding. Heat is to be avoided 

 whenever possible, so that if wax is to be used, the objects should 

 be transferred to carbon bisulphide from alcohol, thence to 

 carbon bisulphide and wax, and left overnight in an oj^en dish in 

 a warm place, and imbedded quickly next day in pure wax. We 

 are often doubtful if the double celloidin wax imbedding method 

 really helps for such objects. But it is certain that the celloidin 

 paint method, while sectioning, is adv^antagcous. 



Fixatives which are particularly good for insects are Carnoy, 

 Petrunkewitsch, alcoholic and ordinary Bouin, and picro- 

 nitric. 



