1925 ] External Anatomy of Head and Abdomen of the Roach 215 
the rectum to become everted, exposing the rectal lining and 
the endorectal plates enp, which are rather weakly-pigmented 
chitinous protections of the rectal folds or bands. The rectum 
protrudes in a similar fashion in specimens of termites, psocids, 
etc., preserved in alcohol, and it is possible that the insects in 
question may be able to protrude the parts voluntarily when 
irritated by the alcohol into which they are thrown when col- 
lected. 
In the foregoing discussion, only the external parts of the 
head and abdomen have been taken up. In a second paper, 
already practically completed, the external features of the 
thorax and its appendages will be discussed; and I am hoping 
to take up the gross internal anatomy as well, in subsequent 
papers dealing with the structure of the roach Periplaneta 
americana. In the present paper, most of the drawings are 
based upon a study of P. americana, ; but in a few instances 
drawings were made from specimens of a closely allied form. 
The parts of the other forms, however, are so similar to those of 
P. americana , that there will be no difficulty in identifying all of 
the structures figured, in studying P. americana , with the figures 
in question as a guide. 
Bibliography. 
ChopaRd, 1920. Segments abdominaux chez Orthopteres. 
Thesis, Paris, 1920. 
Comstock & Kochi, 1902. Head of Insects. Amer. Nat., 36, 
p. 13- 
Crampton, 1916. Orthopterous Maxillae. Psyche, 23, p. 83- 
1917. Head Structures. Ent. News, 28, p. 398- 
1917. Abdomen of Female Insects. Jour. N. Y. 
Ent. Soc. 25, p. 225- 
1918. Male Genitalia. Bull. Brooklyn Ent. Soc., 
13, p. 49- 
1920. Basic Plan of Male Genitalia. Can. Ent., 52, 
p. 178- 
1921. Head of Insects. Ann. Ent. Soc. America, 
14, p. 65- 
