120 T. OKADA 



of the Neo-Adansonian school (Sneath, 1961) or of numerical taxonomy (Sokal and 

 Sneath, 1963). Although much conflict and dispute has been raised between the 

 orthodox or phylogenetic taxonomists and the Neo-Adansonians, the principle 

 claiming overall similarity or using the "greatest possible number of characters" in 

 classification is unequivocally accepted by most of the current phylogenetic as well 

 as numerical taxonomists. The archestinic character should be of taxonomic 

 importance in this context (Kiriakoff, 1965 : 64 ; Mayr, 1965 : 73). 



Some examples of the archestinic characters can be cited from the present investi- 

 gation. The subgenus Dichaetophora of the genus Drosophila has necessarily been 

 characterized by the absence or abbreviation of the anterior dorsocentrals, while 

 D. rotundicornis possesses rather well developed anterior dorsocentrals, which can be 

 explained as archestinic. Likewise, the occurrence of six rows of acrostichal 

 hairs in Chaetodrosophilella coei should be archestinic, because the genus Chaetodroso- 

 philella shows essentially two or four rows of acrostichal hairs (Wheeler and Takada 

 1964). Incidentally, accepting the overall similarity principle, the author agrees 

 with L. H. Throckmorton (personal communication) to treat Drosophila subtilis 

 Kikkawa and Peng, 1938, from Japan as a member of the subgenus Scaptodrosophila, 

 although this species differs from ordinary species of Scaptodrosophila in having no 

 prescutellars. 



B. HOMEOTIC EXPRESSION OF THE HOOKED SCALY BRISTLES 



The " hooked scaly bristles " (Okada, 1963) are special thick bristles of a secondary 

 sexual character found on the male tibia and metatarsus of the mid leg in some 

 melanogaster group species belonging to the suzukii, takahashii, and ficusphila 

 subgroups and in Drosophila (Tanigastrella) gracilis (Duda, 1924) (Okada, 1964b). 

 It was proved that amongst present material, D. (Sophophora) tristipennis and D. (S.) 

 immacularis , both belonging to the suzukii subgroup, also have such bristles. So 

 far as examined by the author, the species possessing the hooked scaly bristles have, 

 without exception, also sex-combs on the male fore legs, but the species having sex- 

 combs do not always possess the hooked scaly bristles. This fact makes it plausible 

 that the occurrence of the hooked scaly bristles pre-requires the possession of the sex- 

 combs and that the development of the sex-combs on the fore leg homeotically 

 induce the hooked scaly bristles on the homonymial organ, the mid leg. The excessive 

 development of the sex-combs, however, seems to diminish the homeotic expression 

 of the hooked scaly bristles through " enantiomorphosis " (Okada, 1960c) or through 

 " material compensation " (Rensch, 1954). The compensation would be manifested 

 in two such structures with the same function as these two kinds of bristles of similar 

 secondary sexual character. The same is true for the reversal correlation found by 

 Prevosti (1954) between the number of sex-comb teeth and of clasper teeth among 

 the species of the obscura group as well as among the natural populations of Droso- 

 phila subobscura Collin, 1936 in Europe. 



The homeotic and compensatory developments of the hooked scaly bristles and 

 sex-combs can be divided into five stages (Text-fig. 328). Stage 1. Both sex- 

 combs and hooked scaly bristles are absent {willistoni and mommai groups) . Stage 



