339 



small vessels passes to tlie end of the wing and there turns 

 upon itself and runs forwards again. Tliese tracheoles, as 

 well as those of the legs, are all markedly twisted and 

 irregular. • 



Meanwhile the thoracic segments have been undergoing 

 further development. The second segment becomes somewhat 

 convex; the first segment grows downwards, and instead of 

 overlying the rear of the head, now comes to assume its 

 proper position as a shield over the neck and front of the 

 thorax. A mechanical explanation of this will be given later 

 (see Muscular System). 



The metathoracic segment retains its insignificant size. 



Having arrived at their maximum size, the thoracic seg- 

 ments and their appendages form a cuticle. This process, 

 which is coincident with cuticle formation over the rest of 

 the body, is quickly followed by the pupal moult. 



The thorax, which has now attained its general adult 

 shape, begins to undergo changes parallel to those that go on 

 in the head, i.e., ridges, grooves, tubercles, bosses or depres- 

 sions, etc., are developed on its surface in the positions in 

 which we see them in the imago. This process takes place 

 on the first day of pupal life, and is soon followed by chitinisa- 

 tion. Already in the thirty-six hour pupa this has pro- 

 ceeded considerably, and the only changes which take iDlace 

 during the remainder of the pupal life consist in a thickening 

 of this chitinous coat, accompanied by a general blackening, 

 following close on the blackening of the head. 



The legs, meanwhile, undergo continued ''differentia- 

 tion'^; they shrink greatly within their cuticle, and the 

 segments become more clearly marked (fig. 16). Already at 

 about six hours after pupation the shrinking has permitted 

 the growth of (protoplasmic) bristles on the surface of the 

 legs; soft claws and spines are soon seen, and the trochanters 

 are clearly visible some twenty-four hours after pupation. 

 Tlie view of Lowne that they are really part of the femur, 

 and that they do not represent a distinct segment, com- 

 parable, for example, to the coxa, or tibia, seems justified 

 by their very late appearance in the pupa, the true segments 

 being clearly visible even in late larval stages. Some twenty- 

 four hours after pupation the legs have practically assumed 

 the external appearance of those of the imago. This is fol- 

 lowed by the secretion of chitin, at first slow, later rapid, so 

 that at the end of two and a half days the legs of the pupa 

 are (to external appearances) identical with those of the 

 adult wasp. 



The wings, also, have continued to develop during this 

 time. First a considerable shrinking takes place, so that the 



