THE CHROMOSOME COMPLEX OF CULEX PIPIENS. 293 ' 
larvge disappeared almost entirely. Perhaps this accounts 
for the more frequent occurrence of Culex in the fairly 
clean water of rain-barrels and drinking- troughs, in spite of 
the fact that, as shown by long experience, the larvge grow 
more quickly in a good culture of C hlamy domonas, and 
that, on this account, one would expect the gnats to prefer a 
more stagnant habitat. 
The egg-rafts, for the cytological studies in question, after 
being laid, which process takes about ten to fifteen minutes, 
were isolated, along with sufficient water from the pond, in 
Petri dishes, in which they underwent their subsequent 
development. Thus it was possible to determine the age of 
the eggs. Rafts just laid, and of ages ranging from half 
hour after the deposition of the last egg to two and three- 
quarter hours, were preserved. Imagines just before, during, 
and after oviposition were also fixed. Many rafts of unknown 
age were necessarily found during the season, their colour 
indicating to a certain extent their age. 
My best thanks are offered to Sr. Carmela, S.N.D., who, 
during my absence in August, went on with the work of 
tending the ponds and fixing the rafts at timed intervals. 
She gives twenty minutes as the period required for the 
laying of one raft. 
Carnoy proved an excellent fixative for both rafts and 
imagines. Bouin and Gilson-Petrunkewitsch were used as 
controls. The rafts did not sink in the former fixative, hence 
the results were not so good, but the Bouin material was 
more easily sectioned. Portions of whole rafts were em- 
bedded in paraffin, and sagittal sections of from 5/* -to 8// 
made of the whole mass. Thus many eggs could be examined 
at once. The funnel (see Text-fig. 1 , f) was removed before 
•embedding. 
Mr. P. Jamieson’s long experience in microtoming was 
placed entirely at my disposal in the matter of sectioning* the 
proverbially difficult dipterous egg, and I should like to express 
my gratitude to him for this help, and also for actually 
cutting many of the sections used in this investigation. 
