DEVELOPMENT. 2 1 
published. His material was secured from Vendue and his experi- 
ments made on the grounds of the Institut Agronomique in Paris. 
His method consisted in inclosing a series of plats so as to avoid any 
possible infection from without and then transferring the progeny of 
each generation to fresh unaffected plats, thus keeping up a contin- 
uous series of breedings, the ordinary breaks being provided against 
by the fresh sowings of grain, so that proper food plants were avail- 
able for each period. Starting with imagos issuing April 5 from 
puparia collected March 12, he obtained a second generation of 
imagos May 30, and introducing these in the second case, found tiies 
of the third generation flying July 1. In like manner the progeny of 
this generation developed adults by August 5; the succeeding genera- 
tion, the fifth, appeared September 4, and on October 18 the first 
individuals of the sixth generation, this last depositing eggs which 
produced larvae that changed to puparia and entered upon the winter 
hibernation. At the same time observations were made upon the suc- 
cession of broods appearing in the inclosed plats supporting the first, 
second, and third introductions, which served as a check upon the iso- 
lated rearings. The separate rearings, however, give the most positive 
evidence as to the possible number of broods, and his conclusions from 
these experiments are that under favorable conditions for development 
the Hessian fly may present as many as six or more generations. These 
generations are distributed as follows : The first occurring from April 5 
to April 25; second, from May 30 to June 15 j third, from July 3 to 
July 20: fourth, from August 5 to September 1; fifth, from September 
10 to October 15; sixth, from October 18 to the end of the season. The 
most of these generations are partial, and the more incomplete are the 
third, the fourth, and the sixth. 
The conditions necessary to such a continuous series of broods are of 
course not present in nature, and Marchal calls particular attention to 
the necessity of proper plants and humidity as conditions which are 
far from being associated in nature. This results in a great irregularity 
for the different individuals. In the absence of proper food plants such 
females as might issue would be unable to perpetuate the species. 
Others deposit upon leaves which may be harvested and the larva' 
perish. Certain puparia directly: in contact with the moist earth pursue 
their development rapidly, others inclosed in dry steins have their evo 
lution retarded. The different generations, therefore, intermix in a \ cry 
irregular manner, and among individuals which fly at the end of the 
year there might well be found those belonging to the third, the fourth, 
or even of a still higher number of generations. The extreme fecundity 
of the insects and this great irregularity of development permit the 
insect to perpetuate itself in spite of a want of natural food plants during 
the period of summer heat and to adapt itself to the conditions o\' the 
season. 
He further points out that in a year presenting for example a moist 
month of July the third generation would almost entirely issue and 
