---- The Species of Mylacris (Ibid). Boston, 1884. 4to.
---- A Review of Mesozoic Cockroaches (Ibid). Boston, 1886. 4to.
---- Triassic Insects from the Rocky Mountains (Amer. Journ. Sc. Arts[3], XXVIII.). New Haven, 1884. 8vo.
---- Systematische Uebersicht der fossilen Myriopoden, Arachnoideen und Insekten (Zittel, Handb. Palæont. I. Abth., Bd. II.). München, 1885. 8vo.
Westwood, J. O. Contributions to Fossil Entomology (Quart. Journ. Geol. Soc., Lond., X.). London, 1854. 8vo.
Like all useful scavengers, the Cockroach is looked upon nowadays as an unmitigated pest. It has, however, a certain right to our regard, for it comes of a venerable antiquity. Indeed, palæontologically considered, no Insect is so interesting as the Cockroach. Of no other type of Insects can it be said that it occurs at every horizon where Insects have been found in any numbers; in no group whatever can the changes wrought by time be so carefully and completely studied as here; none other has furnished more important evidence concerning the phylogeny of Insects. Even the oldest known air-breathing animal has been claimed (though I think erroneously) as a Cockroach; yet, however that may be, it is certain that in the most ancient deposits which have yielded any abundance of Insect remains, the Coal Measures, they so far outnumber all other types of Insects, that this period, as far as its hexapodal fauna is concerned, may fairly be called the Age of Cockroaches. And though the subsequent periods show an ever-diminishing percentage of this family when compared with the total synchronous Insect fauna, yet the existing species are counted by hundreds, and the fecundity of some, attested by every housewife, may be looked upon as a sufficient explanation of the persistence of this antique type. The Cockroach is, therefore, a very aristocrat among Insects.
Our knowledge of its past is derived almost entirely from its wings; perhaps because these organs are the farthest removed from the nourishing fluids of the body, which on death become one of the agents, or at least the media, of putrefaction and consequent obliteration. At all events, whatever the cause, these chitinous membranes, with their network of supporting rods, and even not infrequently with the minutest reticulation of the membrane itself, are preserved with extraordinary fidelity, and in such abundance that, by comparison with similar parts in existing forms, we may reach some general conclusions concerning the life of the past of no little interest.
The first thing that would strike an observer, looking at the ancient Cockroaches, would be their general resemblance to the living. Excepting for their usually larger size,[194] were we to have the oldest known Cockroaches in our kitchens to-day, the householder would take no special note of them—unless, indeed, the transparency of their wings (shortly to be mentioned) were to give them a somewhat peculiar aspect. There would be the same rounded pronotal shield, the same overlapping wings, coursed by branching veins, the same smooth curves and oval flattened form of the whole creature, and doubtless also the same scurrying movements. Indeed, some accurate observers—so, I suppose, we must call them—have failed to take note of some important and very general distinctions between the living and the dead. Thus Gerstaecker, in a work begun twenty years ago, and not yet finished, said, near its beginning,[195] “Not a single species of Insect has yet been found in the Carboniferous rocks which does not fall, on closer examination (mit voller Evidenz), not only in an existing order, but even almost completely in the same family as some living form, and only presents striking distinctions when compared with the species themselves.” He further specifies the Cockroaches described from the Coal Measures, by Germar and Goldenberg, as agreeing in every distinguishing family characteristic with those of the present day.
In one sense, indeed, this is true. We separate the living Cockroaches from other kinds of Orthoptera as a “family” group, and “Cockroaches” have existed since the Coal Measures at least; yet the structure of every one of the older types is really so peculiar that none of them can be brought within the limits of the family as it now exists. We recognise ours, indeed, as the direct descendants of the ancient forms, but so changed in structure as to form a distinct group. A parallel case is found in the Walking-sticks, and is even more obvious. The recent researches of M. Charles Brongniart have brought to view a whole series of forms in Carboniferous times, which are manifestly the progenitors of living Walking-sticks, with their remarkably long and slender stick-like body, attenuated legs, and peculiar appendages at the tip of the abdomen. Existing forms are either wingless or else have opaque elytron-like front wings, and very ample, gauzy, fan-like hind wings; while the Carboniferous species are furnished with four membranous wings, almost precisely alike, and so utterly different from those of existing types that, before the discovery of the bodies, these wings were universally classed as the wings of Neuropterous Insects (sensu Linneano). Thus Gerstaecker, in the very place already quoted, says of these same wings, known under the generic name Dictyoneura, that they show at least a very close relationship to the Ephemeridæ of to-day.