1 88 PSYCHE [Oct. — Dec. 



THE TIPULII) HYPOPVGUJM, A STLJDV IN SPECIFIC 

 ADAPTATIONS. 



BY ROBERT E. SNODGRASS, STANFORD UNIVERSITY, CAL. 



A detailed study of the terminal abdominal segments of the males and females 

 of the Tipulidae shows an enormous amount of variety in the hypopygial parts of 

 the males, and, in striking contrast, a uniform simplicity of structure in the corre- 

 sponding parts of the females. The writer has made such a study on a large num- 

 ber of Tipulid species in the entomological collection of the Washington Agricul- 

 tural College, identified by Mr. R. W. Doane. The detailed descriptions and 

 figures are comprised in two papers not yet published, but some facts of general 

 interest are here given. 



The term " hypopygium " may be most conveniently limited to the ninth abdom- 

 inal segment of the male. This is the genital segment, /. e., the one that in all 

 insects carries the intromittent organ and usually the clasping appendages. 



The Tipulid hypopygium is in general cup-shaped with the opening posterior. 

 The cavity of the cup is \\\^ genital chamber and is produced simply by the invagi- 

 nation of the posterior face of the segment. This necessarily carries into the 

 genital chamber the tenth or anal segment which, morphologically, terminates the 

 abdomen. Attached to the posterior rim of the hypopygium are, on each side, 

 from one to three clasping lobes, called the apical appendages. The body of the 

 segment is composed of four plates — one dorsal, one ventral, and two lateral. The 

 dorsal and ventral plates are evidently the tergum and sternum respectively, while 

 the lateral ones may be termed the pleural plates on account of their position. In 

 the lower genera they have strictly a pleural position, but in the higher genera they 

 may be simply set into the posterior rim of the segment, or exserted upon the pos- 

 terior margin, or they may be lacking entirely. They always, however, when pres- 

 ent, bear the apical appendages. According to the structure of the pleura the 

 relationships of the larger groups within the family and the evolution of the genera 

 from one another may be nicely traced. 



Within the genital chamber and arising from its floor or anterior wall lies the 

 penis, a straight or curved rod-like tube. Its terminal part is always protected by 

 a chitinous guard arising from the posterior part of the floor of the genital chamber. 



Now, although the larger groups within the family are separable on a basis of 

 modifications in the more fundamental parts of the hypopygium, the other parts, 

 such as the apical lobes, the penis, and the guard of the penis, present an infinite 

 number of specific variations. No two species, no matter how similar otherwise, 

 were found to be even nearly identical in the structure of these parts. 



