and Position of the Hymenoptera. -Qi 



and in having more or less clearly defined sutures between the 

 pieces composing the head. The eggs of the different species 

 compared presented no appreciable differences. 



In the pupa state, the two sizes of male, female, and workers 

 can be more readily appreciated than in the imago state, as the 

 insects can be more easily measured and comparisons made. 

 Corresponding cases of dimorphism in other insects will probably 

 be studied to great advantage when the insects are observed at 

 this period of life. Between the two sizes of the ? in the pupa 

 of Bombus fervidus there was a difference of '05 inch, and in 

 thcc^ -03 inch. In a number of the worker pupae oi Bombus 

 separatus there was a difference of '04 inch between the two 

 broods of workers, the more advanced brood being smaller, and 

 not only shorter but also narrower. 



In this connexion we would present some views relative to a 

 theory of the number of arthromeres composing the head of 

 Insects {Hexapoda), and the number and sequence of their ap- 

 pendages, suggested by studies of the larval forms of Hymeno- 

 ptera, and especially the lower Neuroptera, not omitting insects 

 belonging to other suborders, and some forms of Crustacea, 

 After Savigny had shown that the mouth-parts of Insects and 

 Crustacea were jointed appendages like those attached to the 

 thorax, and therefore repetitions of an ideal jointed limb or ap- 

 pendage, Audouin proved that in the ideal arthromere, of which 

 the bodies of all Articulata are each a congeries arranged in a 

 longitudinal series, the periphery should be distinguished into an 

 upper {tergite, Duthiers), lower {sternite, Duthiers), and pleural 

 part, and that in the thorax the legs were thrust out between the 

 pleurite and sternite, and the wings grew out between the pleu- 

 rite and tergite. The arthropleural region is therefore the 

 limb-bearing region of the body, and the different parts of the 

 ideal ring are developed in a degree subordinate to the uses of 

 the limbs and wings. Thus in the walkers, such as the Cara- 

 bidse, the pleural and tergal regions are most developed ; while 

 in those insects, such as the Dragonflies, which are constantly 

 on the wing, and rarely walk, the pleural region is enormously 

 developed, and the tergites and sternites attain to their minimum 

 development. The muscles used in flight are greatly increased 

 in size over the atrophied muscles brought into requisition by 

 the act of walking. In the Hymenoptera, however, which are 

 both walkers and fliers, the three portions of the ring are most 

 equally developed. 



These parts of the arthromere are simplest in the abdomen, 

 and become more differentiated in the thorax, where the nume- 

 rous pieces composing them have been classified and named, 

 mostly by Audouin, M*Leay, and Lacaze-Duthiers. Scarcely 



7* 



