156 
Proceedings of the Royal Society of Edinburgh. [Sess. 
The egg s were fixed in Bles’s fluid, but as the envelopes are exceedingly 
impervious, it was found necessary to puncture them to permit the fixative 
to penetrate. The punctures were made in two opposite places, with fine 
needles, under a dissecting microscope. The early stages had to be sectioned 
without removal of their envelopes, which would have involved injury to 
the peripheral parts ; but it was found that only sagittal and transverse 
sections were practicable, the brittleness of the envelopes rendering it 
impossible to cut sections parallel to the wide surfaces of the egg. Later 
stages could be cut in this direction, as the envelopes could be easily 
removed from them, especially after the material had been hardened in 
alcohol. 
As the eggs are minute and transparent, it was found desirable to stain 
them with alcoholic eosin before embedding them in paraffin. Cedar-wood 
oil was used as a clearing agent. For embedding, the simple apparatus 
and rapid method recommended in Stephen’s and Christopher’s Practical 
Study of Malaria was employed. Their description is as follows: — “The 
embedding apparatus is simply a slab of copper 12 x 3 x J ins. Heat this 
at one end, and place the vessel containing the paraffin at a point on the 
slab where the paraffin is just kept melted. This is the temperature for 
embedding.” Obviously the eggs had to be watched throughout the 
process, about forty-five minutes. 
Sections were stained with Heidenhain’s iron alum and hsematoxylin, 
or by Mann’s eosin and toluidin blue method. (One per cent, water-soluble 
eosin solution, fifteen minutes ; one per cent, solution of toluidin blue, three 
minutes. Differentiate in absolute alcohol, five minutes.) 
Internal Structure of the Egg and the Early Development. 
Sections of freshly deposited eggs show, lying immediately beneath the 
inner pellicle, a clearly defined layer of cytoplasm, characterised by its 
finely and densely granular nature. This is the periplasm. The granules 
are remarkably uniform in size, and, stained with Heidenhain’s iron alum 
hmmatoxylin, they appear all of one tint, but in sections stained in eosin 
and toluidin blue, and well differentiated, the periplasm is seen to be 
composed of two strata, of which the inner one — next the yolk — is of 
irregular thickness and much more tenacious of the blue stain than the 
peripheral one, from which the blue is readily washed out, leaving a 
pink layer which is thickest towards the anterior end of the egg, narrow- 
ing towards the posterior end. Internal to the periplasm the egg is filled 
by the yolk-plasma, forming everywhere a network, enclosing the three 
elements recorded by most other observers of the eggs of insects : — (1) 
