Structure and Life-history of the Holly-fly. 273 
leaf at the place of weakness which has been made ready 
for the escape of the fly. We have not attended to the 
ichneumon parasites of the holly-fly further than to note 
that there are two distinct species at least, one appearing 
early in June and the other later in the summer. We 
have found parasitic larve in holly-fly larve of all ages, 
but are unable to say when or how the eggs are deposited. 
Cyclorrhaphous and Orthorrhaphous Diptera.—The larval 
skin, which forms the wall of the puparium, is marked by 
prepared lines, which facilitate the escape of the fly. In 
the holly-fly one line begins on the prothorax, just below 
the spiracle, passes horizontally back to the fore-part of 
Chie ee OEE TEE DT old Frtriin 
Peale Mh Lire peg 
tll by tah Pastel ne 
i TT 
i Oath 
nl 
rT 
I 
! 
| 
Fie. 12. 
Fly emerging from puparium. (x 20.) 
the 1st abdominal segment, and there forks into a descend- 
ing and a slighter ascending branch. It will be convenient 
to speak of these lines as “lines of dehiscence.” * In the 
holly-fly the horizontal line of dehiscence, together with 
the descending one, marks out a triangular ventral plate, 
which can be turned back as on a hinge to allow the fly 
to escape. In Drosophila a similar horizontal line of 
dehiscence runs along the thorax, and then forks as in the 
holly-fly. Here, however, the ascending branch is the 
* Such lines have been called “sutures,” a term which is open to 
objection, because it suggests the line of union of distinct morpho- 
logical elements, as in the phrase “sutures of the skull.” They 
differ, on the other hand, from lines of fracture in being prepared in 
advance ; they can be traced in a puparium from which no fly has 
emerged. 
