. Anniversary memoirs of the Boston society of natural history ; pub. in celebration of the fiftieth anniversary of the Society's foundation. 1830-1880. Natural history; Indians of North America. OF THE MILK-WEED BUTTERFLY. 13 This latter organ is a dark, horny, slightly curved tube, about 6 mm. in length. The tip expands into a small trumpet shaped mouth, which is twisted more or less asymmetri- cally. At rest, the tip lies between, and a little beyond the triangular flaps of the anal somite, just below the anus, and is inclosed in a membranous sheath (ps.), to permit of its protrusion beyond
. Anniversary memoirs of the Boston society of natural history ; pub. in celebration of the fiftieth anniversary of the Society's foundation. 1830-1880. Natural history; Indians of North America. OF THE MILK-WEED BUTTERFLY. 13 This latter organ is a dark, horny, slightly curved tube, about 6 mm. in length. The tip expands into a small trumpet shaped mouth, which is twisted more or less asymmetri- cally. At rest, the tip lies between, and a little beyond the triangular flaps of the anal somite, just below the anus, and is inclosed in a membranous sheath (ps.), to permit of its protrusion beyond the body. This protrusion is worked by two extensor muscles (), one on each side, whose attachments and mode of action will become sufficiently evident by the inspection of fig. 16. The ventral arch of the ninth somite sends a process into the abdomen immediately underneath the penis, for the support of the latter, and the attachment of a large band of muscular fibres () which embraces the penis, holds it in place, and accomplishes its re- traction. The External Male Armature iisr the Lepidoptera. The secondary male organs of the Lepidoptera are constructed on a simple plan, which is modified after various fashions ia the different groups, and these modifications are often serviceable as characters of classificatory importance. Their typical structure is well illustrated by the Satyrid but> terflies, (see the adjoining figure), in which the dorsum of the anal or ninth abdominal segment is produced into a simple term- inal hook directed downwards, recalling the telson of Crusta- cea. The sternum of the same somite is reduced to a narrow, U-shaped piece, which may be called the ventral arch. To this ventral arch are articulated two, more or less pincer-like, clasp- ^ , , „ . )) A n 1 11 External armature of Saty- mg organs, termed simply " claspers. As already stated, the rws a?ope, male; (/.dorsum, and anus lies just beneath the hook, and the penis projects be
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