BOTE THE SEXES IN DIPTERA. 371 



to Lnwne *, most probably tbe method by which the common Cockroach, Feriplaneta 

 orieiitalis, Linn., is fertilized. 



Homologies of the Genitalia in Periplaneta orientalis and Diftera. — With the view of 

 homologizing the genitalia of the two orders, I liave made a number of dissections of 

 this P. orientalis^ and have come to the following conclusions. The greatest difficulty 

 of the investigation was the unsymmetrical character of the parts. 



1. The whole combination, which in all the other insects that I have examined is 

 always in the longitudinal plane of the abdomen, in Feriplaneta is placed in a transverse 

 position. What Lovvne calls the left gonapophyses (the spiuus titillatorius) is usually 

 the most anterior part of the genitalia. 



2. Though there is no duct opening in a penis, there are parts which represent the 

 theca, the hypophalius, and the paraphalli. 



3. The part which I homologize with the hypophalius is highly chitinized, has a 

 structure of short triangular serrations similar to that on the same part in the Blow-fiy — 

 a structure which is constantly recurring in the different families of Diptera (PI. 25. 

 fig. 41 ; PI. 26. fig. 68 ; PL 29. fig. 101). 



4. These are grouped round the "conglobate gland" of Professor Miallf, the 

 paraphalli forming the " saddle-shaped piece." 



5. Opposite and distinct from these organs, on the right side of the insect, is a 

 mechanism of a number of pieces forming a receptacle and fitted with a plate which 

 acts as a lid. Below this, and supporting the base, is an apodeme which, from its 

 structure and situation, I homologize with the ejaculatory apodeme in Dij)tera, more 

 particularly as it is found in the Tipuliuae. 



6. There are also pieces which, though they are not symmetrical, represent tlie 

 forcipes interiores, and a hairy process which shows the site of an atrophied palpus. 



7. The important great apodemes are difficult to find and equally difficult to display 

 in a preparation. On either side of the left-hand part of the genitalia (the penis and 

 its appendages), and forming part of the membrane at the bases, are two insignificant 

 islands of chitin quite surrounded by a sea of wrinkled, transparent membrane. They 

 appear to be functiouless, and are nearly suboval plates, tapering to a point. Their 

 microscoi)ic structure is consistent with my idea that they are the atrophied remains 

 of the apodemes. 



These complete the list of pieces in the left-hand part, with the exception of a small 

 subtiiangular piece at the base of the titillator, which appears to be some part of its 

 articulation to the theca. 



A species of Braehijtrupes has genitalia very difi'erent from Feriplaneta. They arc 

 symmetrical ; there is a central stilil'orm simple penis, which appears to have the opening 

 of the ductus ejaculatorius at its extremity. This is surrounded by a theca, bearing 

 forcipes interiores and palpi genitalium, fused to it. A pair of lateral apodemes are 



* ' Blow-fly,' p. 664. 



t ' The Cockroach,' 5Iiull and Doiiiiy, p. 174. 

 SECOND SERIES. — ZOOLOGY, VOL. IX. 54 



