72 
Psyche 
[June 
wings, enough whole specimens have been found to give us 
a slight knowledge of their body structure. They were 
primitive insects, probably more so than any other known 
winged insects, but they did have some specializations. 
It should be noted, in this connection, that no remains of 
bodies of any insects have been found in the older half of 
the Upper Carboniferous strata. Not until we come to the 
Mazon Creek deposits, about 15 million years after the 
first record of the insects, are body remains known. This 
probably would have provided ample time for extensive 
specialization to develop. At any rate, the Palaeodicty- 
optera were more primitive than any winged insects now 
living. They show about the same range in size as living 
dragonflies, many having a wing expanse of about two 
inches. The head was relatively small ; the mouth-parts 
mandibulate and inconspicuous. Their antennae are un- 
known, except for the proximal segments ; probably they 
were moderately long and multisegmented. The thoracic 
segments and legs were nearly homonomous. The most 
striking characteristic of the Palaeodictyoptera was the 
presence of paired membraneous lobes on the prothorax ; 
these resembled miniature wings and are usually con- 
sidered liomologues of the functional meso- and meta- 
thoracic wings. The abdominal segments showed little 
differentiation, and the abdomen terminated in a pair of 
long, multisegmented cerci. Well preserved specimens 
have paired lateral lobes on each abdominal segment. 
The immature stages of the Palaeodictyoptera are com- 
pletely unknown. Several vague and fragmentary speci- 
mens, which are probably insect nymphs of some sort, 
have been assigned to the Palaeodictyoptera, but they 
could just as well belong to certain other groups. The 
paired abdominal lobes of the adult have been generally 
interpreted as vestigial tracheal gills of the nymphs. 
This of course implies that the nymphs were aquatic ; and 
in view of the close relationship between the Ephemerida 
and Odonata, both of which have aquatic nymphs, we may 
infer this to have been the case. From this you will see 
that our knowledge of the Palaeodictyoptera is not great. 
Their general activities were probably much like those of 
