18 ENTOMOLOGICAL SOCIETY 



Pore Formula of Merocheta. 



Strongylodesmus.... 5 ... 7 8 9 10 n 12 13 14 15 16 17 18 19 



Helodesmus 5 ... 7 8 9 10 n 12 13 14 15 16 17 



Gomphodesmidse (numerous 



genera), Eurydesmus 5 ... 7 ... 9 10 n 12 13 14 15 16 17 18 19 



Polydesmus and nearly all 



genera not noted here 5 ... 7 ... 9 10 ... 12 13 ... 15 16 17 18 19 



Napodesmus, Hynidesmus, 



Cylindrodesmus, Brachy- 



desmus, Scytonotus 5 ... 7 ... 9 10 ... 12 13 ... 15 16 17 18 ... 



Cynedesmus 5 ... 7 ... 9 10 ... 12 13 .. 15 16 



Comodesmus 5 ... 7.. .9 12 15 .. 17 18 



Heptadestnus* 5 9 12 15 ... 17 18 19 



Batodesmus 5 9 ... ... 12? 15?-.. 17? 



Psochodesmus 5 ... 7 ... 9 12 13 ... 15 



Stenodesmus, Biporodesmus, 



Duoporus 5 



Pterodesmus, Xanthodesmus 7 ... 9 10 ... 12 13 ... 15 16 17 18 19 



Since in all other orders of Diplopoda the repugnatorial pores 

 occur in uninterrupted series, that -condition may be considered 

 to have been ancestral in the Merocheta as well. The unrelated 

 monotypic genera, Strongylodesmus from Mexico, and Helodes 

 mus from Java, approximate a continuous series, the sixth segment 

 being the only break. The South American genus Eurydesmus, 

 and numerous East African genera of Gomphodesmidaa, have but 

 two interruptions, segments 6 and 8. The formula of Polydes- 

 mus is, however, that which on account of its very general prev 

 alence, is looked upon as normal for members of this order, 

 occurring as it does in families the most diverse in other char 

 acters. With the exception of those of the genera mentioned 

 above, all other formulae may be considered as reductions of that 

 of Polydesmus, the absence of pores from segments 6, 8, n and 

 14 being invariable. 



Not only is there diversity in the number and distribution of 

 the repugnatorial pores of the Merocheta, their position on the 

 segments and the attendant structural modifications are equally 

 varied and as little likely to have been brought about by any 

 advantage pertaining to the different conditions. Some are close 

 to the margin, some remote ; some elevated on tubercles or stalks, 

 others sunk in depressions. But these details are merely illustra 

 tions, not arguments, since on no one character or set of char 

 acters could a negative proposition be established. The case 

 must rest on the phylogenetic, biologic and ecologic unity of the 



* A new genus of Oxydesmidae from West Africa. The type is H. con- 

 nivens (Cook), described as Scytodesmus connivens. Brandtia, p. 10, 1896. 



