INSECTA. 



243 



long and slender oesophagus, y, conveys the fluids to the chylific 

 stomach, and to a v/ide crop {fig. 105. k\ which during the pupa 

 J05 state has been gradually 



expanded from one side 

 of the end of the gullet. 

 The chylific stomach (g) 

 has shrunk into a compa- 

 ratively short fusiform 

 cavity, which is still cha- 

 Sphinx Ligustri. Imago. racterised by the trans- 



verse sacculi and constrictions. The small intestine (/) has dimi- 

 nished in width, but increased in length, and now lies in several con- 

 volutions between the chylific stomach and colon, the upper part 

 of which has also been produced into a cascum (m). The biliary ves- 

 sels are diminished in length, but still communicate, by a short com- 

 mon duct on each side, with the commencement of the small intestine. 



In the bee the metamorphosis of the digestive organs is still more 

 striking than in the butterfly, inasmuch as the alimentary cavity con- 

 sists, beyond the short and wide oesophagus, exclusively of a large 

 transversely plicated chylific stomach without intestine or vent. 



The larvae of bees and wasps have from four to six biliary vessels, 

 which shrink in diameter and contract in ength during the pupa state. 



The gizzard is never present in the vermiform larvae of the Coleop- 

 tera, although usually possessed by the perfect insect. 



In the larvae of the Scarahm^ Melolontha, and most herbivorous 

 Coleoptera, the chylific stomach is shorter than in the imago ; but it is 

 furnished at both ends with caecal appendages, which disappear during 

 the metamorphosis, except in the genus Hister^ in which some traces 

 remain in the perfect insect. 



The salivary vessels of the caterpillars of the Lepidoptera are of two 

 kinds ; one pair is short and broad, sometimes vesicular, as in the 

 Cossus ligniperda, and their ducts terminate at the base of the max- 

 illae. Those of the second pair are very long and slender, occupying, 

 with their longitudinal coils, the sides of the abdomen, and sending 

 their slender ducts forwards to unite together and terminate upon a 

 peculiar prominence upon the under lip, which is called the spinneret.* 

 These tubular glands, though classed with the salivary apparatus, are 

 peculiar, in their full development, to the larvae, and are called " se- 

 ricteria " or silk-tubes, because they prepare the glutinous material, 

 or silk, which the larva spins to form its cocoon. In the perfect in- 



See preps. Nos. 2985. to 2988. 

 R 2 



