408 A. J. NICHOLSON 
The dorsal surface and the portion of the envelope lying under 
the floats are covered with very different processes. They are 
longer, and thin sheets of chorion radiate from a central axis, 
so that in section the processes are star-shaped. At the top 
of each process a cap-like structure joins all the radiating thin 
sheets together (fig. 41). 
At the line of division between the dorsal and ventral types 
of processes there is a single row of much longer processes which 
extend as a band from the terminations of the floats to the tips 
of the ege (fig. 9). 
The fourth type of process only occurs in small numbers and 
is found at each end of the egg. This type is a comparatively 
large boss-like structure consisting of a solid mass of chorion, 
and seven or eight are found at the extreme anterior and 
posterior ends of the egg (fig. 40). 
The floats consist of a single sheet of chorion attached to 
the chorion envelope along its ventro-lateral surface only. 
The sheet curves round till it almost touches the dorso-lateral 
surface so enclosing a considerable cavity. The whole of the 
chorion sheet which forms the float is highly corrugated 
(fig. 9). 
The whole of these structures, with the possible exception of 
the ‘ bosses’, appear to serve the purpose of supporting the 
ege on the surface of the water. The ventral processes enclose 
a film of air, which cannot be expelled by the water owing to 
its surface tension and the closeness of the processes to one 
another. The floats enclose a relatively large volume of air, 
and again surface tension prevents the entrance of water. The 
band of long processes, from the floats to the tips of the egg, 
probably helps to support the egg by making use of surface 
tension directly, i.e. by lying on the surface film of water. 
The comparatively long dorsal processes do not help to 
support the egg normally, but if an egg is sunk it will be 
found that the relatively thick film of air enclosed by these 
always causes the ege to regain the surface with its dorsal 
surface uppermost. 
If a drowning mosquito lays its eggs under the water it-is 
5d! 
