236 Prof. J. C. Schiódte on the Morphology 
answer is that Cryptocerata (Pelegoni, Nepæ, Naucorides, 
Corixæ, Notonecte) are not united together except by features 
which are connected with their life under water, and that 
Nepe on the one side, and Notonecte and the other families on 
the other side, are not less different from each other in all 
points of their structure than Dytisci and Hydrophili amongst 
Eleutherata. In Nepe the posterior limbs are moved alter- 
nately, as in Hydrophili; like these latter, they crawl and 
climb and row about; and in both families peculiar modifica- 
tions of certain organs are required in order to facilitate respi- 
ration—in Hydrophili of the antennæ, in Nepe of the last pair 
of spiracles: in Naucorides, Corixe, and Notonecte, on the con- 
trary, the movement of the posterior limbs is isochronic, as in 
Dytisci ; they are like these typical swimmers ; and no special 
simply an error: Cryptocerata have undivided thoracic seg- 
ments like all the 8 
sternum and epimera is never to be found. Nor is it dif- 
ficult to trace the origin of the mistake. The fact is that each 
oup of muscles belonging to the limbs moulds that part of 
the thorax to which it is attached into a separate form ; an 
the lines of demarcation between these divisions project inter- 
nally in proportion as the muscles are stronger; these boundary- 
lines appear outside as slightly impressed lines, and, on account 
of their thickness in the depth, they appear with a darker colour 
when the background is light. The water-bugs, being supported 
by the medium in which they live, do not require such thick in- 
teguments of the thorax as those which live on dry land; their 
colours are never very dark, never metallic, but generally grey 
or yellow, in consequence of which the integuments are more 
even, smooth, and lamelliform than in land-bugs, and the 
boundary-lines between the parts occupied by different sets of 
muscles far more striking to the eye. It is likewise an erro- 
neous appreciation of facts when it is stated that the metathorax 
in Corixe is furnished with “ parapleure" (that is, epimera 
. 
; ? : 
separate from episterna); for the coxe do notatallarticulate with 
