OF THE MILK-WEED BUTTERFLY. 11 



thorax, and with no chamber : and hence at first I thought that the features presented by 

 Archippus were peculiar to its family, or perhaps to the butterflies. I have, however, since 

 dissected Vanassa Hunter a,^ a sphingid and a noctuid, and found the same conditions as in 

 the Milkweed Butterfly, so it is probable they are characteristic of the Lepidoptera, as one 

 would indeed expect from the general uniformity in the anatomy of the group. How 

 Newport in his minute and numberless dissections could have overlooked so striking a fea- 

 ture remains inexplicable, unless we presume that his figure represents what he took 

 for granted to be the case rather than what he saw. The pulsating ventral blood sinus 

 I have not studied in Archippus. 



Nervous System. Newport's beautiful monograph^ of the nervous system in Sphinx 

 ligustri renders anything more than a brief description of its main features, as shown in 

 fig. 2, unnecessary. The brain {hr.) immediately overlies the oesophagus, occupying nearly 

 the centre of the head and giving rise to the optic and antennal nerves. The commissures 

 between it and the next or suboesophageal ganglion, forming the oesophageal nerve-collar, 

 are short and stout. From the latter ganglion ax'ise the nerves of the mouth organs. The 

 thorax contains only two ganglia in the perfect insect, two of the original three thoracic 

 ganglia having been fused into one during pupation. The first of them, that is the second 

 post-oral ganglion, is the smaller, and nearly round, the next being double its length and 

 oval. The important nerves arising in the thorax are those of the leg pairs, and those of 

 the wings. The latter arise from the nerve cord between the two ganglia. 



The second to the sixth abdominal segments each contain a ganglion ; these gradually 

 increase in size to the last, which is compound and of considerable size. 



The stomato-gastric nerves are not shown in the figure owing to their small size and dif- 

 ficulty of representation. A small ganglion, the frontal ganglion, lies in front of and 

 below the brain hemispheres, with which it is connected by a recurved cord on either side. 

 Posteriorly it gives off a single median coi'd, the 7iervus recurrens, which jDasses back- 

 ward over the oesophagus and through the oesophageal nerve-collar. A pair of ganglia 

 also lie behind the brain hemispheres, connected with the nervus recurrens. The latter 

 runs backward over the oesophagus, innervating it and the dorsal vessel. On reaching the 

 stomach it divides into three branches, which run over and either side of this organ. 

 Branchlets are also given off to the food-reservoir. 



Female Organs of Reproduction. The external opening of the oviduct (o.o.) is sit- 

 uated immediately below the anus and hardly separated from it, between the lappets of 

 the ninth segment. It leads into a short oviduct, which near the middle of the seventh 

 segment divides into two lateral branches, each of which is about as long as the common 

 duct, and each in turn gives rise to the four branches forming the ovaries. These ovarian 

 tubes from their union in the sixth segment run forward almost to the third segment, just 

 above the stomach ; they then curve upward and run backwards to the end of the sixth, 

 again curve upwards and pass forward into the fourth segment, when their slender tips 

 become solid cords, gradually unite together, and become attached to the dorsal wall of 



^Mr. Scudder informs me that in dissections of chrysalids of Z). ago, he observed and noted these peculiarities of the aorta. 

 Archippus, Vanesxa lo and other butterflies, made some years ■'Phil. Trans. 1834. 



