rackard.] 



280 



much liiglier up tlie 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 posi- 

 tion of the posterior pair of wings, so important in a morphological 

 point of view, is accompanied by a corresponding change in the pro- 

 portions of the thorax. The meta-thorax has become mostly absorbed, 

 so as to resemble more the same parts in the pupa ; while the meso- 

 thorax retains much of its original proportions, though becoming 

 more compact, 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, antennae 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 important central parts, and 

 proceeds outwards to the periphery. 



In this stage (Fig. 1), when the mouth-parts of the semi-pupa have 

 become solid enough to enable the larval head to be stripped oif with- 

 out 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 out- 

 line of the eyes is distinct, but they are not raised above the surface 

 of the head. The antennae, clypeus and mouth-parts, collectively, 

 form a second anterior portion separated by a curved line from the 

 epicranlum. It is this anterior portion which lies in the larval head in 

 this stage. The great increase of size of the appendages of the 

 semi-pupa have forced forward the hard crust of the larval head, 

 which suggested to Ratzcburg* the idea that the head of the pupa 

 was originally composed of the two first rings (I. e., head and protho- 

 rax,) of the body of the larva. The antennaj 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, lying on each side of the labrum with its palpi and 

 the maxillae. These appendages do not as yet project much beyond 

 the antennae, being short and papIUIform, preserving the general form 

 of the same organs in the larvae. 



At this period the elements (sterno-rhahdltes, L. Duthiers,) compos- 



*Ueber Entwicklunc: der fusslosen hymenoptercn larvon. etc. Is'ova Acta Natur. 

 Curios. Tom. xvi. 1832. Westwood has fully shown the fallacy of this idea, (Trans. 

 Ent. Soc. Loudon. Vol. II. p. 121), and our own observations corroborate his 

 statements and conclusions. 



