236 



W. WESCHE ON THE MALE GENITALIA OF THE COCKROACH, 



in the interior of the genitalia are aborted, but there are a 

 number of sensory hairs which indicate the site of the left 

 palpus, while the right has completely disappeared. This remnant 

 indicates by its presence that in some period of the evolution 

 the palpi were fully developed, and that changes have taken 

 place. The functional changes undergone by these parts are, 

 very possibly, the cause of their extraordinary asymmetry; 

 similar conditions are found in Periplaneta americcma, Linn., and 

 a species of Mantis as shown in the descriptions of Mons. A 

 Peytoureau.* 



The exterior parts are less difficult to recognise, as they are 

 symmetrical, but they are very dissimilar from their homologues 

 in other insects, and quite archaic in type, as may be seen by a 

 comparison with the Crustacean Oniscidae (wood-lice). 



I shall now describe each portion of the armature separately, 

 with the nomenclature that has been formulated for the corres- 

 ponding parts in Diptera f ; though this is an inversion of 

 the usual process, yet, as I have endeavoured to show, it is 

 advisable, owing to the exigencies of the case. 



(a) Forcipes inferior es. — These are represented by a sym- 

 metrical pair of simple unsegmented rods with blunt points, 

 inserted in sockets and placed laterally on the ventral side of the 

 abdomen (Fig. 5). 



(b) Forcipes siqieriores. — These I homologise with the cerci ; a 

 symmetrical pair of palpi-like organs with sixteen joints and 

 moderate pubescence, which is more marked on one side than on 

 the other. Some delicate sense-hairs can be seen scattered 

 among the more robust tactile-hairs. One of my preparations 

 exhibits a complicated series of nerves and ganglia, showing that 

 the part fulfils sensory functions, as these organs often do in the 

 Diptera (Fig. 4). 



(c) Lamina superior. — A highly chitinised plate which covers 



the bases of the forcipes superior es corresponds with this. 



* Morphologie de V ar mure genital des insectes, A. Peytoureau. Paris, 1895. 

 f The Genitalia of both Sexes in Diptera. W. Wesche, Trans. Linn. Soc. 

 London. 2nd. Ser. Zool vol. ix., Part 10, 1906. 



