STOUGH: THE HACKBERRY PSYLLA. 159 



ture of an ovipositor as being composed of several pairs of 

 stylets has already been mentioned. 



To homologize the structure of the ovipositor of Pachypsylla 

 with the structure of the typical ovipositor is more difficult 

 than the comparison of it with that as seen in the different 

 families of the Homoptera. I find that it is more specialized 

 than a typical ovipositor such as found in the Orthoptera, 

 though it is possible to show the homologies; but since it re- 

 sembles more closely that found among the Hymenoptera — 

 where it is specialized to form a sting — these homologies can 

 be traced through the latter. Taking the sting of the honey- 

 bee as a type of the hymenopterous ovipositor, since this has 

 been so carefully worked out by Cheshire and others, it can be 

 seen that the lower valves of Pachypsylla (30-1 and 3, Iv) 

 correspond to the lower and outer pair of darts in the honey- 

 bee. The upper valves of Pachypsylla correspond to the inner 

 pair in the bee, where they are fused into one piece to form the 

 sheath. It should be noted here that the sheath does not corre- 

 spond to that part of the ovipositor of Pachypsylla which I 

 have designated by that name. In the honeybee there are two 

 fleshy processes, one on each side of the sting, which are 

 thought to represent the upper pair of stylets and are called 

 the "sting-palpi" or "feelers." These are evidently the same 

 as the lateral tongues found in Pachypsylla. 



The homologies up to this point are comparatively clear, 

 but as to the remainder of the parts I can only theorize, as 

 their structure is complicated and there are present more 

 pieces than in the typical organ. The lateral tongues evidently 

 are the "sting-palpi" and together with the lateral rods and 

 lateral plates form the upper pair of stylets; but this expla- 

 nation does not account for the median rod with its processes 

 and appendages. There may be three possible explanations 

 for these structures: 



1. This median rod might be regarded as a fusion of the 

 dorsal pair of stylets, and the rods and lateral plates only as 

 tendons causing the spreading of the sc 1 and sc 2 and conse- 

 quently the sting-palpi. 



2. The rods and lateral plates might be considered as com- 

 posing the dorsal pair of stylets and the median rod as an 

 accessory structure which, moving backward and forward, 

 would spread and close the sting-palpi, for these latter are 



