The male reproductive organs of Insects, in spite of very great superficial diversity, are reducible to a common type, which is exemplified by certain Coleoptera. The essential parts are (1) the _testes_, which in their simplest form are paired, convoluted tubes; more commonly they branch into many tubules or vesiculæ, while they may become consolidated into a single organ; (2) long coiled _vasa deferentia_, opening into or close to (3) paired _vesiculæ seminales_, which discharge into (4) the _ejaculatory duct_, a muscular tube, with chitinous lining, by which the spermatozoa are forcibly expelled. Opening into the vesiculæ seminales, the ejaculatory duct, or by a distinct external orifice, may be found (5) _accessory glands_, very variable in form, size, and number. More than one set may occur in the same Insect. To these parts, which are rarely deficient, are very often appended an external armature of hooks or claspers. The male Cockroach will be found to agree with this description. It presents, however, two peculiarities which are uncommon, though not unparalleled. In the first place the testes are functional only in the young male. They subsequently shrivel, and are functionally replaced by the vesiculæ seminales and their appendages, where the later transformations of the sperm-cells are effected. The atrophied testes are nevertheless sufficiently large in the adult to be easily made out. Secondly, the accessory glands are numerous, and differ both in function and insertion. Two sets are attached to the vesiculæ seminales, and the fore end of the ejaculatory duct (_utriculi majores_ and _breviores_); another large conglobate gland opens separately to the exterior. We shall now describe the structure of these parts in more detail.[168] [168] We propose to notice here the chief differences which we have found between the figures of Brehm (_loc. cit._), which are the fullest and best we have seen, and our own dissections. Figs. 10, 11 (pp. 169–70). The ejaculatory duct and duct of the conglobate gland are made to end in the penis (_infra_, p. 178). Figs. 14, 15 (p. 173). These figures seem to us erroneous in many respects, such as the median position of the penis and titillator. Fig. 16 (p. 174). The pair of hooks marked _E_ are too small, and there are additional plates at the base, which are not figured (see our fig. 102). _F_ (of our fig.) is omitted.