=The penis.=—This is a single or double median style-like structure either hollow and perforated, or solid, very variable in shape, receiving the end of the ejaculatory duct. It is usually enclosed between two lateral plates, the homologues perhaps of the inner pair of sheaths of the ovipositor. In the Coleoptera, as in Carabidæ and Melolonthidæ, the penis is a long chitinous tube, “retractile within the abdomen on the under surface as far as the anterior segments.” (Newport.) In the Hymenoptera, of which that of the saw-flies is a type, Newport states that it “consists of a short valvular projectile organ, covered externally by two pointed horny plates (_i_) clothed with soft hairs.” Above these are two other irregular double-jointed plates (Fig. 202, _l_) surrounded at their base by a chitinous ring (_k_); they are edged with prehensile hooked spines (_i_). Between these in the middle line are two elongated muscular parts (_m_) which enclose the penis (_h_), and which, like those in beetles, perhaps aid in dilating the vulva of the female. An examination of Figs. 203–207 will aid in understanding the various modifications in beetles, etc., of this organ. A general study of the anatomy and homologies of the male genital armature, from a developmental point of view, together with a comparison of them with the corresponding female organs, is still needed. [Illustration: FIG. 203.—End of abdomen situated under the anal lobes of _Hydrophilus piceus_, drawn out, seen from the ventral side: 6, sternal region of 6th segment; 7, 8, 9, segments telescoped, when retracted, in 6th segment; _zw_, membrane connecting 6th and 7th segments; _G_, intromittent apparatus; _vl_, external lobes; _vlu_, inner lobes; _pn_, penis. ] [Illustration: FIG. 204.—The same as in Fig. 203, seen from the side: 6, the free 6th segment; 7–10, the four last, when at rest, retracted and telescoped within the 6th segment, with the copulatory apparatus (_g_); _vl_, outer, _vlu_, inner lobe; 10_s_, tergite of 10th segment; 10_i_, sternite of the same; _an_, anal opening. ] [Illustration: FIG. 205.—Terminal parts of the male copulatory apparatus of _Hydrophilus piceus_, torn apart: _vlu_, the two inner lodes; _pn_, penis; _x_, membrane torn from under side of penis; _ej_, ejaculatory duct; _os_, its opening on the under side of the penis, directly under its tip. The muscles, tracheæ, and nerves are not drawn. ] =Velum penis.=—In the locusts (Acrydiidæ) the penis is concealed by a convex plate, flap, or hood, free anteriorly and attached posteriorly and on the sides to the ridge forming the upper edge of the tenth sternite. When about to unite sexually, the tip of the abdomen is depressed, the hood is drawn backward, uncovering the chitinous penis.