LEPIDOPTERA. 237 



metathorax is much compressed antero-posteriorly. The scu- 

 tum is thrown aside as it were by the scutellum into two lat- 

 eral, nearly square halves, the remaining tergal pieces being 

 usually obsolete and membranous, but in Sthenopis the prse- 

 scutum and scutellum (Fig. 13, page 12) are large, and meet 

 in the middle of the segment, much as in the neuropterous 

 Sialidce and Hemerobiidce. 



The abdomen is oval in Papilio, becoming long and linear in 

 the Tineids. In the Zygcenidce, especially, the basal ring is 

 membranous and is partly adherent to the thorax, and somewhat 

 inflated on each side. The number of abdominal segments 

 varies, being either eight or nine ; the variation occurring, as 

 stated by Lacaze-Duthiers, in closely allied genera ; thus the 

 genital and anal openings are placed more usually behind the 

 eighth, but sometimes behind the ninth segment. 



The genital armor is very simple, consisting of two valve- 

 like pieces. The parts beyond (anal stylets, etc.) are aborted, 

 so that the anus and external opening of the oviduct are 

 brought closely together. In the male the parts are more com- 

 plex, the anal forceps often, as in the Callosamia Promethea, 

 forming long curved hooks for clasping the abdomen of the 

 female. 



The nervous system of Lepidoptera, and its changes during 

 the transformations of the larva, have been studied most 

 thoroughly by Herold (in Pieris) and Newport (in Sphinx 

 ligustri and Vanessa urticse). In the imago the ventral cord 

 consists of seven ganglia, while in the larva there are eleven. 

 This decrease in their number is due to the fusion, during the 

 pupa state, of the first, second, third and fourth ganglia of 

 the larva, exclusive of those situated in the front part of the 

 head ; these form the two thoracic ganglia which distribute 

 nerves to the legs and the muscles of the wings. Meanwhile 

 the fifth and sixth ganglia of the larva have either disappeared 

 entirely, or been united with the others. 



The digestive system (see Fig. 44, on page 35) of butterflies 

 and moths is modified to suit their peculiar habits. They draw 

 in the sweets of plants through the "tongue" by a sucking 

 stomach which opens into the hinder end of the oesophagus. 

 4 'The ileum is long, small, and nearly always forms several 



