EXTERNAL ANATOMY OF INSECTS. 579 
the trunk and legs of Hexapods. In the Octopod Aptera 
and the Arachnida the trunk consists of a single piece, 
not separated from the head, and sometimes not distinct 
from the abdomen. 
V. Internal processes*. Perhaps you will think that 
this head would be better considered when I treat of the 
Internal Anatomy of Insects ; but as the parts included 
under it are really processes of the external integument 
of the trunk, it seemed to me best to treat of them under 
that head. ‘They are of two descriptions; processes of 
the thorax or upper part of the trunk, and processes of 
the breast or its under part. 
i. Processes of the thorax”. ‘These are the phragma, 
prophragma, mesophragma, and metaphragma. ‘The first 
belongs to the prothorax, the second to the mesothoraa, 
and the two last to the metathorax ; each forming a kind 
of chamber of the under-side of each segment of the 
thorax. 
1. Phragma. The phragm, or septum of the protho- 
rax, is most conspicuous in the mole-cricket (Gryllotal- 
pa), in which it is a hairy ligament attached to the inside 
of the upper and lateral margins of the base of that part: 
inclining inwards, it forms the cavity which receives the 
mesothorax. It is not, however, without a representa- 
tive in many Coleoptera, though in these it is less striking, 
from its being smaller and taking a horizontal direction. 
In Elater, by means of some prominent points received 
by corresponding cavities of the vertical part of the base 
of the elytrum, it forms a kind of ginglymous articula- 
* Prate VII. Fic. 3. x’. IX. Fic. 2. 5’. and XXII. Fic. 5—14, 
> Prate XXII. Fic, 8—11. 
Pt 
