10 BURGESS ON THE ANATOMY 



{ileum, i.), a tube about one-quarter of the diameter of the former, running first backwards, 

 then upwards and forwards, then turning backwards again, thus making a flattened S- 

 curve in the fifth and sixth segments. The intestine in this course passes to the left of 

 the bursa copulatrix of the female, and of the testis and penis in the male (see figs. 2 and 

 14, i). The intestine passes, in the dorsal region of the sixth segment, into the colon, or 

 large intestine (c), which in some Lepidoptera is expanded anteriorly into a large coecal 

 sac. In the milk- weed butterfly the colon is somewhat pyriform in the female (fig. 2, c), 

 but is longer and more cylindrical in the male (fig. 14, c). It is dotted over with numer- 

 ous little glands of doubtful function.' The colon narrows posteriorly and is followed by a 

 short cylindrical division, the rectum (r.). The anus (a.) opens between the triangular lap- 

 pets of the ninth segment. 



The Haemal System. The hea7't (h.) is a small tube lying immediately under the dor- 

 sal wall of the abdomen, and hung in this position by triangular muscular sheets (the 

 alary muscles), which are placed in pairs, apices inwards, on either side of the heart. The 

 walls of the heart contain two sets of muscular fibres running spirally in opposite direc- 

 tions. Slight constrictions divide the heart into a number of segments, corresponding to 

 those of the abdomen. Each segment has probably a pair of clefts for the entrance of the 

 blood, but I have not succeeded in clearly making out their exact number.^ 



In the basal segment of the abdomen, the heart narrows slightly, making the begin- 

 ning of the aorta {ao.). This after entering the thorax runs upwards, passing between 

 the right and left sets of thoracic muscles, and then under the suture between the mesoscu- 

 tum and scutellum, and expands rather suddenly into a large chamber (ao.c), which is 

 huno" in position by a net-work of fibrous connective tissue. This aortal chamber is some- 

 what pear-shaped, with the greater diameter posterior. The forward end bends downwards 

 aAd again contracts into a slender tube, which runs backwards and downward until it 

 reaches the first part of the aorta, and after passing along the anterior face of this for a 

 short distance, it bends suddenly forward and runs along, and just above, the oesophagus, 

 passing with the latter into the head and through the oesophageal nerve collar. The 

 aorta then seems to bend upwards, but I have not attempted to trace it beyond this point.^ 

 The aortal walls, including those of the chamber, are provided with muscular fibres in 

 spiral layers, as in the heart. 



The aorta is very readily demonstrated throughout its whole course, and the chamber 

 forms a conspicuous object in a good longitudinal section ; it is therefore ver}' remarkable 

 that its peculiar character * should have hitherto escaped the notice of anatomists. New- 

 port's figure of Sphinx ligustri^ represents the aorta distinctly following the curve of the 



iPor the structure of these glands, see Chun, Abhandh d. cacy. Anterior to these trunks are two smaller ones, which 



Senckenb. Naturforsch. Gesellsch. Bd. x. ■ appear to be joined to the parts of the mouth and antennae, 



^Newport (Cycl. Anat. and Phys. Ii, 977) states that there and nearer the median line are two others which are contin- 



are eight pairs of openings in Sphinx ligustri. nations of the aorta. These pass upwards and are lost in 



s Newport (Cycl. Anat. and Phys., II, 978) says of Sp. the integuments." 

 Iigufl7-i and Vanessa uriicae "the aorta after passing beneath ■* No other case in which any portion of the aorta runs 



the cerebrum gives off laterally two large trunks, which are backwards has been described among insects, nor in which it 



each ecjual in capacity to about one-third of the main vessel. dilates into a chamber. Cornalia (ISIonografia del Bombix 



These pass one on each side of the head, and are divided del Gelso. Mem . 1st. Lomb., vi. 4°. IMilano, 1856) figures 



into three branches, which are directed baekward, but have a slight dilatation, but no recurving, in Bombyx mori. 

 not been traced farther in consequence of their extreme deli- ^ Phil. Trans. 1834, pi. xiv. 



