164 Mr. R. Shelford on new 
means evident at first sight. A knowledge of the habits of 
an animal should invariably precede all suggestions as to the 
value of any details of its structure, and I feel convinced that 
much of the mystery surrounding variations in structure 
which are spoken of as being merely of importance to the 
systematic naturalist will be dispelled as our knowledge of 
the life-histories of the animals exhibiting them increases. A 
clue to the use of the variations in pronotal structure of the 
cockroaches under notice is afforded by the observations, 
slight and incomplete though they are, on their habits. The 
vast majority of Blattide are insects of cryptic habits, 
spending most of their life hidden under stones or logs, in 
decaying vegetation, burrowing in rotten wood, and so forth, 
and the majority of species are flattened depressed insects. 
The species of Pilema, on the other hand, are convex and 
more or less cylindrical insects with a large heavy pronotum, 
the anterior border of which is often slightly reflexed and 
bounded laterally by the upwardly projecting lateral wings. 
Mr. Distant, in his ‘Insecta Transvaaliensia,’ has recently 
published an interesting field-observation on the habits of a 
species identified as Pilema thoracica, Walk. A female 
accompanied by several larve was taken from the bottom of 
a neat round hole in the ground about 6 inches in depth ; 
there were half a dozen such holes in about half an acre, and 
all contained families of this species. I have no doubt but 
that all the species of this genus have adopted this mode of 
life, and that the pronotum is the part of the body that is 
used in excavating the burrows, for on examining some 
specimens of P. refleza, Walk., and P. hebetata, Sss. & Z., 
in the British Museum, I found that in these the channel 
between the pronotal disk and lateral bands was simply 
choked with earth. It is not unreasonable to assume that 
the heavy shovel-like pronotum of Pilema has been evolved 
in response to a change of habitat. ‘Turning now to the 
other end of the series of cockroaches considered, we find 
that the species of Derocalymma are the most flattened 
members of the whole family, and in correspondence with 
this depressed form it is no surprise to learn that they live 
under heavy stones. ‘The advantage of the flattened form, 
enabling the insects to slip through narrow crevices and to 
lie in security in a circumscribed shelter beneath a stone too 
heavy for any but a relatively powerful enemy to move, is 
obvious ; and, again, it is not unreasonable to assume that 
the highly moditied pronotum of Derocalymma is a result of 
a change of habitat. There is no information forthcoming as 
to the habits of Bantua and Cyrtotria; some species of the 
