[Illustration: Fig. 162—Wing-nervuration of _Castnia_. Undersides of, A, front, B, hind wings. 1_a_, 1_b_, 1_c_, 1_d_, Inner marginal nervures; 2, lower branch of median; 8, subcostal of hind wing; 12, subcostal of front wing; _e_, "stalk" of 8 and 9; _f_, frenulum; _r_, retinaculum; _s_, shoulder; _g_, articulation of wing.] INTERNAL ANATOMY.[179]—The alimentary canal extends as a long, {320}slender oesophagus through the length of the thorax, dilating when it reaches the abdomen to form a tubular stomach; before this it is somewhat enlarged to form an indistinct crop, and gives off a large diverticulum usually called a sucking stomach. According to Burgess, this structure does not possess the function ascribed to it by this name, and he terms it a food-reservoir. The Malpighian tubes are six in number, three on each side, and each set of three unite to form a common tube opening into the posterior extremity of the stomach; behind them the alimentary canal continues in the form of a slender, tortuous intestine, expanding at the extremity of the body to form a rectum. The dorsal or circulatory vessel commences near the posterior extremity of the body, but in the front part of the abdomen is deflexed to pass under the great phragma into the thorax, where it rises abruptly to the dorsal wall, but is again abruptly deflexed, forming a loop, and is then prolonged above the oesophagus into the head: at the summit of the thoracic loop there may be a dilatation called the aortal chamber. The supra- and infra-oesophageal ganglia are consolidated into a mass pierced by the oesophagus: there is a minute frontal ganglion; the ventral chain consists of three much approximated thoracic ganglia and four abdominal ganglia separated from the thoracic by a long interval. [Illustration: Fig. 163—Internal anatomy of Lepidoptera. Section of the body of a female butterfly, _Anosia plexippus_. (After Scudder.) The portion to the left of the vertical line more magnified. I. II. III. thoracic segments; 1-9, abdominal segments; _a_, antenna; _a_, anus; _ac_, aortal chamber; _ag^1_, etc., abdominal ganglia; _agl^1_, _agl^2_, accessory glands; _ao_, aorta; _br_, brain; _c_, colon; _cp_, copulatory pouch; _cx^1_, _cx^2_, _cx^3_, coxae; _fr_, food-reservoir; _g^1_, suboesophageal ganglion; _h_, dorsal vessel; _i_, intestine; _lm_, area filled by wing muscles; _l.or_, ovary, or egg-tubes of left side; _mv_, Malpighian tube (the two others of the right side cut away, except small portions); _mx_, maxilla; _o_, oviduct; _oo_, its orifice; _oe_, oesophagus; _ov.c_, end of left ovary; _p_, labial palp; _ph_, pharynx; _r.ov_, terminal parts of right ovarian tubes, turned to one side, after the tubes have been cut away; _sd_, salivary duct; _sgl_, salivary gland; _sp_, spermatheca; _st_, stomach; _tg_, thoracic ganglia; _v_, copulatory orifice.]