364 THE AMERICAN NATURALIST. [VOL. XXXV. 
longer; in the case of Lasius flavus, for example, from the 
first warm spring days until the beginning of June or even 
longer. In the case of the insects, like the flies, with 
a short time devoted to metamorphosis, there must be 
space made for the new organs as quickly as possible ; that 
is, the old larval organs must get out of the way as soon 
as may be. The natural process, a gradual degeneration, 
is a process of long duration, and on that account not suffi- 
cient in the case of the flies. Hence, says Karawaiew, there 
has arisen the barbaric devouring of the tissues by the 
leucocytes. 
It has seemed to me unfortunate that in the study of the 
postembryonal development of the Diptera so much attention 
should have been given to the highly specialized Muscidae and 
so little to more generalized members of the order. The 
metamorphosis of Coretha, Culex, and Chironomus has been 
studied somewhat, but without any approach to that exhaust- 
iveness which characterizes the studies of Weismann, Van 
Rees, Kowalevsky, e£ al., on Calliphora. In the hope of find- 
ing some new light upon these extraordinary phenomena of 
histolysis and histogenesis which are a part of insect meta- 
morphosis I have undertaken the study of the postembryonic 
development of two flies belonging to the more generalized 
Diptera, the Nematocera. One of these flies is Blepharocera 
capitata, a member of the strange, small family, Blepharoce- 
ride, with strangely and strongly modified immature stages, 
and the other is Z7o/orusia rubiginosa, a giant crane fly 
(Tipulidz), with simple immature stages. While both of these 
forms are nematocerous Diptera, and to this extent allied, 
there is an exceptionally wide divergence between them in 
point of structure of the larval stages, and this differ- 
ence has, to my mind, an allimportant influence in deter- 
mining the obvious and suggestive differences in the character 
of the development, which, we shall see, obtains. This 
present reference to the metamorphosis of these two dip- 
terous forms has to do solely with the peculiarly interesting 
and suggestive conditions of the histolytic processes in the 
metamorphosis. r 
