and Position of the Hymenoptera. 91 
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 2 in the pupa 
of Bombus fervidus there was a difference of ‘05 inch, and in 
the § ‘03 inch. In a number of the worker pupe of 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 
hmb-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- 
bidee, 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 mmimum 
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 see aes. Scarcely 
