1935 ] 
Structure of the Pretarsus 
9 
Order Embioptera 
Oligotoma sp. (Fig 6) 
In this order we again find the Blattid type; the planta 
is more extended laterally and is in contact with the basi- 
pulvilli on either side. There is no arolium and the flexor 
membranes are large and slightly expanded. There seems 
to be nothing particularly outstanding about the claw-seg- 
ment of this insect but in general it approaches that of the 
Plecopteran to such a degree as would not prohibit the con- 
ception that these two orders are related. 
Order Plecoptera 
Pteronarcys dorsata Say (Fig. 7) 
Pteronarcys shows the lateral basipulvilli and median 
planta as found in cursorial Orthoptera and termites. The 
arolium is a large and complicated structure which is made 
up of three lobes : a median portion or true arolium, and two 
lateral smaller pads beneath the claws which may be sec- 
ondary divisions of the arolium or pulvilli which have be- 
come fused with the arolium. A more complete study of 
the Plecoptera may settle this question if intermediate forms 
can be found. On the other hand, it is possible that this 
structure represents a new development with no traceable 
homologies to the parts referred to above. (This also ap- 
plies to similar lobes beneath the claws of many Homoptera 
and Hemiptera, to be discussed later). Dorsally, the mem- 
branous pads are supported by chitinous plates (indicated 
by broken lines) and the median lobe bears two clusters of 
small setae on its ventral surface. The presence of planta 
and basipulvilli make it unlikely that the Plecoptera should 
be considered with the Archipterygota. 
Saltatorxal Orthoptera 
Locustidae — Melanoplus bivittatus Say (Fig. 8) 
A large arolium has been found in all Locustids observed 
as contrasted to Tettigoniids and Gryllids in which this 
structure probably does not occur. It should be noted that 
the presence or absence of an arolium is not a condition 
which is constant for an order, but further study should 
