14 



membrane next to the sclerite. The situation in A is primitive, the situation in B is derived. 

 The derivation which B shows as compared with A can be interpreted in two different 

 ways: (1) In ß the insertion of the muscle has shifted from the sclerite to the membrane. 

 (2) In B the sclerite has diminished and has "lost" the insertion of the muscle. According 

 to (1) the sclerites of the two species are homologous in a strict sense. According to (2) 

 they are homologous only in part, since in species B part of the sclerotisation has been 

 lost. In one peculiar case the special circumstances can suggest an interpretation according 

 to either (1) or (2). In many cases, however, an objective decision in favor of one of the 

 two alternatives is hardly possible, and it is debatable whether a discussion of such a case 

 is of importance at all. The interpretation will then be done in that way which seems to 

 be more suitable for the explanation of homology relations. 



3. GENERAL DESCRIPTION AND MORPHOLOGICAL DISCUSSION OF THE 

 POSTABDOMEN AND OF THE MALE GENITAL REGION OF DICTYOPTERA 



The postabdomen of male Dictyoptera comprises the abdominal segments 9-11 and the 

 telson, which contains the anus (Snodgrass 1937). Matsuda (1976) postulates a twelfth 

 segment for the ground-plan of insects, and this would also affect the interpretation of the 

 Dictyopteran postabdomen. According to Matsuda himself, p. 52, however, this "segment" 

 contains neither mesoderm rudiments, nor ganglion rudiments, nor appendage rudiments. 

 Thus, it does not fulfil either criterion to be regarded as a segment. This "twelfth segment" 

 could be regarded as a (highly reduced) segment, if it is demonstrated to be homologous 

 with a true segment (containing mesoderm) of another group of Arthropoda, having lost 

 its segmental organs secondarily. This, however, has not been shown. Therefore, the 

 twelve-segment-theory of Matsuda is not followed here. 



Subsequently the general morphology of the postabdomen and the phallomeres of Blattaria 

 and Mantodea will be described. This will essentially be a description of the common 

 ground-plan of Blattaria and Mantodea, whose reconstruction will be substantiated step 

 by step later on in this paper. 



3.1. The cuticular elements 



Abdominal segment 9 



The sternite of segment 9 (subgenital plate, S9 in fig.320, 321) always forms a large lobe- 

 hke extension to the posterior, which reaches or even exceeds the morphological posterior 

 end of the body (with the anus Af in fig.320, 321c). Most species have a large membranous 

 or only weakly sclerotised area in the anterior half of the subgenital plate (M in fig.320, 

 321b,d,k). The (heavier) sclerotisation is continuous in antero-posterior direction only in 

 the lateralmost parts, to the left and to the right of area M (fig.321k). The lateral parts of 

 the subgenital plate (S91 in fig.321k) curve upwards. The posterior edge of the subgenital 

 plate bears styli (S9s in fig.320, 321b,d,k). 



Along the anterior margin of the subgenital plate the interstemal membrane connecting 

 sternites 8 and 9 adjoins and bends back sharply to the posterior margin of sternite 8 



