and Position of the Hymenoptera. 83 
the labium projects a little beyond the head, owing to the in- 
creased size of the mouth-parts over those of the larva. 
At this period, the two pairs of wings are very equal in size, 
the posterior pair but little smaller than the anterior pair, and 
inserted much higher up the ring nearer the median tergal line 
of the body; and in the succeeding stage the posterior pair are 
seen to be scarcely smaller than the anterior pair, and exactly 
parallel in their insertions, their longitudinal diameter, and their 
tips. This change in the position of the posterior pair of wings, 
so important in a morphological point of view, is accompanied 
by a corresponding change in the proportions of the thorax. 
The metathorax has become mostly absorbed, so as to resemble 
more the same part in the pupa; while the mesothorax retains 
much of its original proportions, though becoming more com- 
pact and presenting less of the tergal area. 
During this time the head has also greatly increased, especially 
in the size of the appendages; the eyes, antennz, and mouth- 
parts begin to assume the size and shape of those of the pupa. 
Development here, as in the thorax, begins in the most impor- 
tant central parts, and proceeds outwards to the periphery. 
In this stage (fig. 1), when the mouth-parts of the semipupa 
have become solid enough to enable the larval head to be stripped 
off without lacerating the extremities of the appendages, the head 
is seen to be divided into two portions. The basal region or 
body of the head, which is lodged under the prothorax of the 
larva, is orbicular when seen from the front; and its sides are 
continuous with the sides of the thorax, as is also the vertex, 
which is likewise of a continuous slope with that of the anterior 
tergal portion of the thorax. Seen from the side, there is no 
separation as yet between the head and thorax. The outline of 
the eyes is distinct, but they are not raised above the surface of 
the head. The antenne, clypeus, and mouth-parts collectively 
form a second anterior portion separated by a curved line from 
the epicranium. It is this anterior portion which hes in the 
larval head in this stage. The great increase of size of the ap- 
pendages of the semipupa have forced forward the hard crust 
of the larval head, which suggested to Ratzeburg the idea that 
the head of the pupa was originally composed of the first two 
rings (2. e. head and prothorax) of the body of the larva*. The 
antennze are flattened down upon the surface, resting on each 
side of the small trapezoidal clypeus, over the front edge of 
which they again meet, when they are flexed upon themselves, 
* Ueber Entwicklung der fusslosen Hymenopteren-Larven, &c.” (Nova 
Acta Natur. Curios. tom. xvi. 1832). Westwood has fully shown the fal- 
lacy of this idea (Trans. Ent. Soc. London, vol. ii. p. ]21); and our own 
observations corroborate his statements and conclusions. 
