The Progress of the Hessian Fhj. 
441 
regular succession of generations, three in the one case and 
four in the other, but that the intermediate generations are 
irregular and fortuitous. Nor are these intermediate genera- 
tions of much consequence to crops, as at the time of their 
development the straw is hard and cannot be attacked, though 
they probably serve to carry on the continuity of existence upon 
self-sown plants, or seedlings. Of course it is possible that the 
recurring generations described by Dr. Lindeman may be 
simply due to the retarded development of individuals, which is 
exemplified in the case of puparia in confinement. 
If it is considered that sound deductions cannot be drawn 
from such artificial circumstances, it may be urged that retarda- 
tion of development is common in most insects, and is a pro- 
vision of nature to prevent the extinction of a species by sudden 
or extraordinary climatal changes or other catastrophes. The 
natural, or normal, period of the existence of the Hessian Fly 
is about 48 days, according to the experience of entomologists 
in America and Russia. But between the egg-laying in the 
spring, which takes place immediately after the fly comes from 
the pupa-case, and the appearance of the fly in the autumn, 
there are far more than 48 days. It may be accepted as a fact 
that the spring generation is not evolved at the same time ; that 
there is not, in short, a general flight from the pupa-cases. 
Nor does the autumn generation by any means appear in its 
winged form simultaneously. There would seem to be no 
reason why there should not be a supply of winged individuals 
of retarded development throughout the season, and this may 
easily be mistaken for distinct generations. In the course of 
time this will be accurately ascertained. It is not considered 
important from an agricultural point of view, as tending to 
make the Hessian Fly more dangerous and destructive, whether 
there are more than two generations in a year. After all, the 
generations to be feared by agriculturists are, that which is 
heralded by the fly in autumn when the wheat is just up, and 
that of the spring when the barley is just springing. 
When the Hessian Fly was first discovered, some farmers 
suggested that its presence should not be made known, as it 
might hinder the sale of their produce. This idea was quickly 
dispelled, and farmers have been very ready to furnish full 
particulars. The Commissioners appointed by the Government 
had not the least difficulty in getting information concerning it 
from them, and they seem willing to adopt any practical 
measures of prevention that may be advised. 
As to measures of prevention, not very mur,h that is new has 
been recommended since those put forth by Miss Ormerod, and 
by the Agricultural Department, which naturally are those 
