between the Insects of the temperate and torrid zones. [199] The wingless creature from the Carboniferous deposits of Saarbrücken, described by Goldenberg as a Cockroach, under the name of _Polyzosterites granosus_, appears to be a Crustacean. We began this review with the statement that no Insect was so important palæontologically as the Cockroach. This would more clearly appear had we space to pass in review the geological history of all the Insect tribes; for then it could be shown that it was only in the passage from palæozoic to mesozoic times that the great ordinal groups of Insects were differentiated, and that the Triassic period therefore becomes the expectant ground of the student of fossil Insects. Up to the present time we do not know half a dozen Insects besides Cockroaches from these rocks. Yet, notwithstanding this advantage on the part of the Cockroaches, how meagre is the history, how striking the “imperfection of the geological record” concerning them, the following tabulation of the fossil species by their genera will show. It here appears that there are about 80 species known from the palæozoic rocks, two or three more than that from the mesozoic, and only nine from the cænozoic! When we call to mind that half the palæozoic Insects were Cockroaches, and that seven or eight hundred species exist to-day, what shall we say of the paltry dozen[200] from the rich tertiaries? Shall we claim that these figures represent their true numerical proportion to their numbers in the more distant past? Then, indeed, must the palæozoic period have been the Age of Cockroaches; for all research into the past shows that a type once losing ground continues to lose it, and does not again regain its strength. The Cockroaches of to-day are no longer, as once, a dominant group; they are but a fragment of the world’s Insect-hosts; yet even now the species are numbered by hundreds. If this be a waning type, what must its numbers have been in the far-off time, when the warm moisture which they still love was the prevailing climatic feature of the world; and how few of that vast horde have been preserved to us! The housekeeper will thank God and take courage. [200] This includes all possible forms; our table shows but nine. GEOLOGICAL DISTRIBUTION OF FOSSIL COCKROACHES. Figures in _italics_ represent the number of American species; in roman, of European.