118 Annuls Entomological Society of America [Vol. XI, 



although he would not lay this down as a fundamental principle. 

 He gives Notonecta as an example of a case where he maintains 

 that there is one pair of cerci on the eleventh somite, another 

 pair on the ninth, and on somites cephalad of these he thinks 

 there may be rudiments of others. His classification of cerci 

 is as follows: the ones found on the eleventh somite, he calls 

 acrocerci, or cerci; those on the tenth, mesocerci; and those on 

 the ninth, procerci. The views of other authors are few in 

 number, and have many points in common. Haase considers 

 them as feeler-like appendages of the "Analstiick" ; Verhoeff, 

 true, segmental appendages of the tenth abdominal somite; 

 Peytoureau, dorsal appendages of the tenth abdominal somite 

 which may be compared, he thinks, with wings in their method 

 of development. 



Heymons and Wheeler in Orthoptera, and Heymons in 

 regard to Dermaptera, Ephemerida, Odonata, and Thysanura 

 agree that cerci are true appendages of the eleventh abdominal 

 somite. 



All of the foregoing opinions except Heymons' s may be 

 grouped together in that all their authors agree that the cerci 

 are appendages, of one kind or another, belonging to the ter- 

 minal abdominal somite. Heymons always regards the ter- 

 minal anal somite as the telson, or twelfth abdominal somite, 

 so would regard the cerci as appendages of the eleventh, or 

 pre-anal somite., Verhoeff lays great stress on the fact that the 

 cerci must be segmented to be true cerci, comparing their 

 segmentation with that of the thoracic legs. Haase and Hey- 

 mons maintain that there is no relationship between the seg- 

 ments of these two structures as such, but rather a far-reaching, 

 " weitgehende," according to Heymons — parallel between the 

 cerci and the antennas, not only in their present form, but in 

 their ontogeny. It is certainly true that the cerci, generally 

 speaking, bear a superficial resemblance to the antennas, but 

 they may also assume, physiologically, entirely different roles. 

 Thus, for example, they may be purely sensory, but they may 

 also be modified as accessory copulatory organs. 



Cholodkovsky was the first, in 1891, to uphold the fact that 

 the cerci were morphologically true pedal extremities, and it is 

 the one place where Heymons can agree with him, as well as 

 with Wheeler and others, that a pair of appendages which may 

 properly be included under the genitalia has its origin in the 



