252 Some Observations on the Egg of Psylla mali 



be seen when eggs are taken of? a twig for observation. For further 

 investigation it was found necessary to make use of special methods 

 of preparation. 



Methods of Preparation. 



Treatment with 10 per cent, caustic soda. If the egg-covered twig be 

 immersed for several days in cold 10 per cent, caustic soda it is possible 

 to withdraw the egg from the plant tissues in which it is imbedded 

 without injury to it. The soda softens the plant tissues and in the 

 space of a few days does not destroy the structure of the larva. In 

 some cases by careful manipulation with mounted needles it was 

 possible to withdraw the larva with its accompanying membranes 

 from the egg shell but usually the larva came away with only one 

 membrane. 



Treatment with bleaching powder solution. In order to study the 

 relation of the egg membranes with more certainty it was found necessary 

 to use some substance that would attach chitin. The most convenient 

 was a mixture of concentrated bleaching powder solution and 10 per cent, 

 caustic soda in about equal parts. This mixture when filtered from 

 the precipitated hydroxide of calcium gives what is practically Eau 

 de Labarraque with excess of soda. By judicious use it is possible 

 to attack the outer chitinous membrane so as nearly to dissolve it 

 without materially injuring the internal structures. 



' Mounting. In most cases concentrated carbolic acid with a small 

 proportion of added glycerine was used. This mixture clears well 

 and gives preparations sufficiently permanent for observation. 



Material. 



As it was desired to study the relation of parts of the larva and 

 egg it was necessary to collect material just before hatching commenced. 

 It was accordingly collected in the middle of April and preserved in 

 alcohol. 



One difficulty in this investigation was the very small number 

 of perfectly formed advanced embryos that could be found. Other 

 writers have pointed out the frequent presence of numerous empty 

 egg shells, but in addition to this I found large numbers of eggs that 

 appeared fairly normal to the naked eye but which proved on further 

 examination to be much retarded in development. It is probable 

 that these eggs were arrested in growth since the normal egg was just 



