418 Dr. David Sharp oh the structure of tlie 



in Aspongopus ohscurus. In the Plataspince they appear 

 at first sight to be absent, but I have succeeded in de- 

 tecting them in nearly all the species I have examined in 

 the shape of curvate, slender, more or less minute, 

 spines, placed one on each side of the protuberant boss 

 formed by the curiously metamorphosed cauda. 



The inferior process. — The usual form for the inferior 

 process to take is that of a ridge or carina, extending 

 transversely across the floor of the j)osterior chamber 

 behind the oedeagus, and immediately below the terminal 

 orifice of the cauda : this ridge may be depressed in the 

 middle, or even quite divided into two separate parts by 

 a deficiency in the middle, or by the division of the lip 

 of the chamber into two lobes. On the other hand, the 

 inferior process in certain species takes the form of a 

 raised acuminate ligula, shaped much like the terminal 

 portion of the bowl of a spoon ; this is well seen in the 

 Tesscratomince. 



The thcca. — The theca is always present, so far as I 

 have observed, except in Paxilochroma lata, where it is 

 apparently wanting. Like the other male parts here de- 

 scribed, it varies greatly in different species in size, texture, 

 and other points. It forms a fence surrounding the cedea- 

 gus, and open at the top to permit the passage of the true 

 intromittent organ through the cedeagus. But in Eclessa 

 rufo-marginata the theca closely embraces, and in fact 

 forms part of, the oedeagus ; and in Pcecilochroma lata, 

 alluded to above, I have little doubt that the lower part 

 of the oedeagus, as shown in fig. 22 a, is really the theca, 

 in which case this insect differs from other forms here 

 described in that the theca is placed below the oedeagus 

 instead of around it. 



The function of the theca is no doubt like that of the 

 rectal-cauda, to serve as a protection to the oedeagus, 

 which it completely surrounds, except at the extremity. 

 There is some evidence that the special duty of the theca 

 may be to protect the oedeagus from the weight and 

 pressure of the rectal-cauda. This evidence is as follows : 

 — So far as I have yet observed there is only one Penta- 

 tomid — Po'cilochrovia lata — in which the oedeagus is 

 not covered by the cauda, but stands up free and exposed 

 behind the very short cauda. Now, this species is also 

 the only one I have discovered in which the theca is 

 apparently absent ; but it would appear that if the theca 



