and Position of the Hymenoptera. 87 



of the internal organs, which is simply a continuation of the 

 outer tegument, or arthroderm, is, in the process of moulting, 

 sloughed off with that outer tegument*. 



Whereas before the head and thorax together were but little 

 more than one-half as large as the abdomen, now they are con- 

 jointly nearly equal in size to the abdomen (fig. 3). The greatest 

 changes have gone on in the two anterior regions of the body. 

 They unitedly tend to assume a spherical form, while the elon- 

 gated abdomen is shortened and very perceptibly altered in form, 

 approaching near that of the pupa, and the whole body is 

 flexed more upon itself. 



The head is still closely appressed to the prothorax, but much 

 less so than formerly, since the increasing size and different 

 proportions of the prothorax have pushed it away. This act of 

 separation has effected an important change in the position of 

 the head as related to that of the rest of the body. It is now 

 truly vertical. Before, its greater length was more continuous 

 with the longitudinal axis of the body, that is, nearly horizontal, 

 or rather inclined at a slight angle from the longer axis. The 

 horizontal position is normal in the lowest insects, as the Neu- 

 roptera. In the Hymenoptera the longer axis of the head is 

 most completely vertical. 



The head in its size, and the development of the appendages, 

 including the mouth-parts, now begins to resemble those parts 

 in the pupa. The eyes are larger and more distinct than before; 

 the maxillae and antennae, though still very short, are shaped 

 more like those parts in the pupa. In the antennae, the most 

 marked change takes place in the three basal joints, or the 

 "scape," of which the second joint now becomes the longest 

 and somewhat contracted in the middle and round at the extre- 

 mity ; while the terminal joints are still doubled upon them- 

 selves, and rest folded upon the mouth-parts. 



The thorax also resembles that of the pupa, though longer; 

 and the basal ring of the abdomen (propodeum) is still exposed 

 to view when seen from above. At this stage the praescutum 

 of the mesothorax, before very distinct, is no longer seen, as in 

 the pupa it is mostly absorbed and passes out of sight, though 

 in the Tenthredinidae it is a large and conspicuous portion of 

 the mesonotum. 



Most interesting changes have occurred in the hinder part of 

 the thorax. Whereas in the previous stage the mesoscutellum 

 was immersed in the ring to which it belongs, it is now elevated 

 and becomes very prominent ; the thorax posteriorly falls rapidly 



* It remains yet to be proved whether the bili.ary tubes, salivary glands, 

 and inner genital glands and cavities form exceptions to this rule. 



