392 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



segments — a little more than three segments long. Its cephalic 

 end is rounded and often slightly enlarged. The remaining por- 

 tion runs straight caudad, increasing in diameter for two thirds 

 of its length and then tapering to its union with the gizzard. The 

 whole structure has a transversely wrinkled wall. 



The position of the Gizzard (plate XXI, figure 1) is peculiarly 

 different in the many specimens dissected: in the females it lies 

 normally in the. second segment in front of the ventriculus, but in 

 the males it seems to be projected caudad into the ventriculus for 

 just two-thirds the latter 's length. It was not positively as- 

 certained that this is a sex difference but some fifteen or twenty 

 specimens were dissected with this result, though one male was 

 found with the gizzard in the second segment. The armature of 

 the gizzard has been well worked out by Miss Higgins (1901) and 

 will not be discussed here. She also records considerable varia- 

 tion in the position of the gizzard in different species and in 

 members of the same species, including some sex differences. 

 These latter, however, neither seem so constant as is true in 

 Lestes ungiiiculatus nor is there any record of such excessive pro- 

 jection into the ventriculus (Op. cit. pp. 131-132). Calopteryx 

 has the gizzard between the third and fourth segments. 



The Ventriculus or Midgut (plate XXI, figure 1, mg.) extends 

 through the fourth, fifth and the greater part of the sixth seg- 

 ments. Its surface is very smooth in both outline and texture, its 

 onh' irregularities being due to the contents of the tract. It is 

 widest (1 mm.) between the fifth and sixth segments, the point 

 occupied by the gizzard in the males; cephalad it is also slightly 

 swollen about the invagination of the gizzard. Encircling its 

 extreme hind end is a whorl of Malpighian tubules. These branch 

 and extend caudad through the seventh, eighth, and part of the 

 ninth segments; they are very closel}^ applied to the sides of the 

 intestine and rectum. Their exact number was not investigated. 



The remaining portion, the Hind Gut, of the Zygopterous 

 alimentary canal is very difficult to interpret without extensive 

 histological work. Tillyard (1917, page 101) makes the statement 

 that it is undivided, but the results obtained by Carroll (1918) on 

 Medstog aster, and Miss CuUen (1918) on Argia moesta putrida 

 clearty prove that this is not the case. No histological examina- 

 tion was made of the Lestes material but several divisions ma}' be 

 made out with the binocular in an ordinary dissection: a long, 



