INTERNAL ANATOMY. 369 



The figures of the internal anatomy were made from dis- 

 sections of alcoholic specimens of the different stages, the 

 work being performed at the entomological laboratory of 

 the Massachusetts Agricultural College. In preparing the 

 material for dissection the insects were first placed for 

 twenty-four hours in fifty per cent, alcohol, then, for the 

 same period of time, in seventy-five per cent, alcohol, and 

 then kept in commercial alcohol until needed for use. The 

 dissections were made under water, by using a small wax- 

 bottomed, dissecting pan. The dissections of the pupte were 

 not wholly satisfactory, since the rapid breaking down of 

 the larval organs and the correspondingly rapid development 

 of the organs of the imago obscured the relations of the 

 difierent parts, and made the correct interpretation of them 

 a difiicult task. The longitudinal section of the pupa, as 

 shown in Plate 58, Fig. 5, is a composite figure, made 

 up from the dissections of several pupse from five to seven 

 days old. 



TJie Alimentary Canal and its Appendages. 



From the medium large mouth' cavity the oesophagus 

 (Plate 58, Fig. 1, oe) leads back through the oesophageal 

 collar formed by a division of the double commissure which 

 connects the brain (b) with the sub-oesophageal ganglion in 

 the first thoracic segment. Here it expands into a peculiar 

 thin-walled organ, which, from its position and size, may be 

 called the anterior stomach (as). This anterior stomach, 

 which is practically an enlarged continuation of the oesoph- 

 agus, is distinctly separated from the posterior stomach, 

 stomach proper, by a well-defined constriction formed by a 

 strong sphincter muscle, possibly valvular in function. 

 The anterior stomach fills the thoracic and a part of the first 

 abdominal segments. A marked distinction from the pos- 

 terior stomach is the fact that it is not supi)lied with the 

 prominent annular muscle bands which are characteristic of 

 the latter organ, although it possesses both annular and 

 longitudinal muscle fibres. In the larger caterpillars it is 

 usually distended by a dark, viscid, semi-fluid mass, con- 

 taining the recently devoured food, and, as shown by micro- 

 scopic examination, numberless bacteria. The posterior 



