OZ MALCOLM EVAN MACGREGOR. 



The females were allowed to oviposit directly on the surface ot water contained in 

 petri dishes, or on to small pieces of filter paper that were floated on the water in order 

 to give the insects a safer foothold than the surface-film presented. These eggs when 

 examined were perfectly normal-looking, but immediately they were removed from 

 the water or off wet paper they began to dry up, with the same shrinkage of the 

 contents, and collapse of the shell. Such eggs when again placed on water and 

 kept at a temperature of 64° F. failed to develop, the embryo having been killed by 

 drying. 



I was therefore left to account in some way for the fact that eggs which had reached 

 London from West Africa had withstood desiccation for over three months, while the 

 eggs laid by the mosquitos here in London were exceedingly liable to destruction by 

 drying. 



Conjecturing the possibility that the eggs when laid might be protected by some 

 substance in the shell that was soluble in or destroyed by water, and that only the 

 eggs laid out of water were able to resist desiccation, the following experiments were 

 undertaken : — 

 Experiment No. I. 



Several fertilised and fully fed females were placed individually in separate glass 

 tubes containing a smaller tube which held a little water and was plugged with filter- 

 paper, to furnish a small damp surface on which the females might be induced to lay 

 their eggs. Oviposition on the filter-paper took place normally about four days after 

 the mosquitos had fed. The eggs w^ere laid during the night, and were examined 

 about 10 o'clock the following morning by means of a binocular microscope, at first 

 in situ, and later after removal to a piece of dry filter-paper. I was surprised to see 

 that the interstices of the wet paper held a much larger amount of water than would 

 have been supposed when looked at w4th the naked eye, and that each egg was in 

 effect lying in a minute pool among the waterlogged paper fibres. The eggs were 

 therefore to all intents and purposes in the same condition as those laid directly on 

 the surface of the water in the petri dishes, and w^hen removed to dry paper began 

 soon afterwards to dry up and collapse in the same way. Accordingly the need of 

 furnishing the mosquitos with something on which they could be induced to lay their 

 >egg6, and which yet held only traces of moisture insufficient to dissolve or destroy 

 any protective substance that might be contained in the egg-shell, became apparent. 



After numerous trials, clover-leaves that had been first thoroughly dried, later 

 stefDed in water until they were soft and pliable, and then pressed between folds 

 of blotting paper until there was little water remaining in the tissues, were found to 

 answer the purpose. 

 Experitnent No. 2. 



A few of the damp clover-leaves were loosely packed into the bottom of small glass 

 tubes, and a fertilised and fully fed female mosquito was imprisoned in each. During 

 the course of a day or two a few eggs were laid by the mosquitos, but all when 

 examined were collapsed. 



Bv the foregoing experiments, the assumption that the shell might contain some 

 substance protecting the egg from desiccation, but which itself was soluble in or 

 destroyed by water, was proved to be wrong, and the problem remained to be 

 explained in some other way. 



