50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



The gnathochilarium has been variously regarded as representing 

 the first maxillae, the second maxillae, and both pairs of maxillae 

 combined. Silvestri (1903) contends that the gnathochilarium is the 

 united first maxillae. According to Robinson (1907), however, there 

 are present in the embryo of Archispirostreptus separate rudiments 

 of first and second maxillae, but the first disappear, and the second 

 alone unite to form the gnathochilarium. In a more recent study on 

 Platyrrhacus amauros, Pflugf elder (1932) asserts that, while two 

 pairs of maxillary appendages are present, they are both combined 

 in the gnathochilarium. The last two writers thus agree as to the 

 number of primary head appendages that are present, but they differ 

 with respect to the segmental connections of these appendages. Robin- 

 son assumes that the segment of the gnathochilarium is contained in 

 the head capsule ; the neck segment, she says, is represented in the 

 embryonic nervous system by a pair of postmaxillary ganglia. Pflug- 

 felder, on the other hand, claims that the second maxillary compo- 

 nents of the gnathochilarium are the appendages of the neck segment, 

 and that the first true body segment is that bearing the first pair of 

 legs. Silvestri also regards the neck segment as the somite of the 

 second maxillae of other arthropods, but he believes that these appen- 

 dages are absent in the Diplopoda. If the gnathochilarium belongs 

 to the neck segment, its muscles should arise in this segment, whereas, 

 according to the description of the head and neck muscles of Diplop- 

 oda given by Silvestri (1903), the muscles of the gnathochilarium 

 take their origin within the head capsule, and the posterior muscula- 

 ture of the head arising on the back plate of the neck segment is 

 very similar to the prothoracic head musculature of insects. There 

 seems to be little support for Silvestri's view that the second maxillae 

 of the diplopods are absent. 



Considering the general similarity of the diplopod head to the 

 cranial capsule of other arthropods, and the evidence of fundamental 

 unity in structure between the several groups of progoneate myria- 

 pods, the current view (see Attems, 1926) is here accepted that the 

 diplopod head contains both the first and the second maxillary somites, 

 and that the legless neck segment is the first body somite, homologous 

 with the first leg-bearing segment of the Symphyla. The legs of this 

 segment are small and reduced by the loss of one segment in Sym- 

 phyla ; in Pauropoda, if present at all, they are rudimentary ; in Diplop- 

 oda they are absent. The genital apertures of the diplopods, we may 

 therefore conclude, are on segment VII behind the mouth, as in the 

 pauropods and symphylids. 



The genital openings in both sexes of the diplopods are more or 

 less closely associated with the bases of the legs of the genital seg- 



