Bordas (1901, 1908) believed that the "conglobate" gland (Miall and Denny, 1886), found in males of _Periplaneta americana_ and _Blatta orientalis_, was an odoriferous gland used for defense, but Gupta (1947) has shown that in all probability this gland (the phallic gland) secretes the outermost covering of the spermatophore. What appears to be mimicry occurs in some species of Blattaria. The nymphs of many Panchlorini and Blaberinae vaguely resemble sow bugs (Chopard, 1938). Certain members of the Perisphaerini (e.g., _Perisphaerus glomeriformis_) from the Malayan region which resemble sow bugs (Annandale, 1900; Hanitsch, 1915) can roll themselves up into a ball thus hiding their antennae and legs (Lucas, 1862). Although these cockroaches are found among dead leaves or under stones, in places in which sow bugs are also found, the benefit to either or both forms is questionable; Annandale (1900) believed that the crustacean and the cockroach, living under similar conditions, developed the same general body shape. Rolling up into a ball is nothing more than an exaggeration of a reflex common to many young cockroaches, that is, an arched position which these insects assume when they immobilize themselves in response to certain stimuli (Chopard, 1938). There are cockroaches that resemble various Coleoptera and Hemiptera (Belt, 1874; Shelford, 1912; Hanitsch, 1915). Some look like cerambycids, lampyrids, coccinellids, pentatomids, etc. Perhaps the most striking examples are the resemblances of cockroaches in the genus _Prosoplecta_ of the Epilamprinae to beetles of the family Coccinellidae; Shelford (1912) has figured a number of species of _Prosoplecta_ together with the species of beetles which they seem to have taken for models. Williams (1928) mentioned diurnal cockroaches which by a combination of markings, shape, posture, and active flight about vegetation suggest certain wasps. Unfortunately, practically nothing is known about the behavior of these so-called mimics and models or their relationships with predators in the field. For the most part, the examples are based on a comparison of pinned insects from museum collections (Burr, 1899); for this reason Chopard (1938) believed that not much value should be placed on superficial resemblances of this kind. However, we believe that a lack of knowledge of cockroach mimicry is not a valid reason for rejecting the idea that mimicry, if it occurs, may be of some benefit in the survival of mimetic species. Certainly Cott's (1940) voluminous compilation of the literature on adaptive coloration should make the most skeptic hesitate to conclude dogmatically that these instances of mimicry are merely accidental and meaningless. XIX. THE BIOLOGICAL CONTROL OF COCKROACHES