449, A. J. NICHOLSON 
only stage of the organism which I have observed and, though 
a number of insects were found affected, the cysts were only 
observed in mature oocytes. 
The nurse-cells of the ovary of one insect were found to be 
heavily infected with diplococei. The follicles were nearly 
fully developed, and IT could observe no harmful effect of the 
bacteria. The infection appeared to be entirely confined to the 
nurse-cells. 
SUMMARY. 
1. The period at which the ovaries of A. maculipennis 
commence to develop depends on the season and locality. 
Normally this is from about the middle of March to the begin- 
ning of April. 
2. A meal of blood appears to be necessary for the production 
of eggs. 
3. One meal of blood is sufficient to cause eggs to be produced. 
After the lapse of a day the large blood-mass in the stomach 
shows two zones: a posterior partially-digested portion and 
an anterior portion of apparently fresh blood. This appearance 
has sometimes been taken as evidence that more than one meal 
of blood has been consumed. 
4, The eggs are fully developed six days after the insect has 
fed on blood. 
5.. In the case of two insects which were observed at the time 
of oviposition the eggs were laid immediately after dark. 
6. The muscle-bands of the ovarian sheaths are striped ; 
not unstriped as is usual in insects. 
7. A large number of vacuolated cells are found in the ovary. 
The nature of these is not clear, but they appear to have some 
relation to the tracheal system. 
8. The chorion of the egg is highly specialized to retain 
air round the egg, and the buoyancy of the egg is entirely due 
to the entrapped air. 
9. The floats are produced by a very specialized form of 
folding of the follicular epithelium. 
