The ABDOMEN differs according to the sex. In the female seven segments are conspicuous dorsally, but only six ventrally, because the first segment is entirely membranous beneath, and is concealed between the second abdominal ventral plate and the posterior coxae. Besides these segments there are at the hind end two others smaller, more or less completely withdrawn into the body, and in certain cases forming an ovipositor. These nine segments are usually considered to constitute the abdomen; but according to Peytoureau,[174] a tenth dorsal plate is represented on either side of the anal orifice, though there is no trace of a corresponding ventral plate. In the male the segments, externally conspicuous, are one more than in the female. According to the authority quoted,[175] this sex has also truly ten abdominal segments, the ninth segment being withdrawn to a greater or {314}less extent to the inside of the body, and modified to form part of a copulatory apparatus; its dorsal portion bears a process called the "uncus"; the anal orifice opens on the inner face of this process, and below it there is another process—developed to a greater or less extent—called the "scaphium." The ventral portion of the ninth segment bears a lobe, the "saccus" (Peytoureau, _l.c._). On each side of the ninth abdominal segment there is a process called the "valve," the internal wall of which bears some hook-like or other processes called "harpes"; it is continued as a membrane surrounding the "oedeagus," or penis, and—bearing more or less distinct prominences—connects with the scaphium. In many forms the parts alluded to, other than the valves, are concealed by the latter, which come together when closed, and may be covered externally with scales like the rest of the abdomen. Peytoureau considers that the uncus is really the dorsal plate of a tenth segment, and that the scaphium is the tenth ventral plate. Thus, according to this view, the ninth segment is extensive and complex, being very highly modified in all its parts: while the tenth segment is greatly reduced. The structure of the male organs is simpler in Lepidoptera, and less varied than it is in the other great Orders of Insects. There are seven pairs of abdominal spiracles on the upper parts of the membranous pleurae. [Illustration: Fig. 160—_Acherontia atropos._ The termination of ♂ body, one side removed. _IX_, Ninth dorsal plate; _IX’_, ninth ventral; _s_, lobe, saccus, of ninth ventral plate; _X_, tenth dorsal plate, or uncus; _sc_, scaphium, or tenth ventral plate; _a_, position of anus; _b_, chitinised band of scaphium; _V_, valve or clasper; _c_, hooks, or harpes, of clasper; _p_, penis (or oedeagus). (After Peytoureau.)]