608 MARGARET EOEINSON. 



mouth parts are only two in number ; namely, mandibles and 

 one pair of maxillfe. Heathcote's (1888) observations con- 

 firm tins statement as also do those of vom Rath (188G), 

 whose dissertation unfortunately I have been unable to see. 

 While Heathcote merely mentions the fact of there being 

 but one pair of maxilla), Metschnikoff insists upon it as being 

 important, and includes it among other points of resemblance 

 between the Poduridae and the Chilognatha. 



More lately, zoologists have been quite awake to the 

 significance of there being only two pairs of mouth parts in 

 the Chilognatha, though but few observations have been 

 made on the development of these myriapods. Folsom (1900) 

 quotes Packard (1883) as saying that there can only be two pairs 

 of oral appendages ; but adds that he (Folsom) would suggest 

 that further embryological studies on Diplopods might show 

 more. In his summary he homologises the Diplopod gnatlio- 

 chilarium with three Hexapod somites, namely, those of the 

 superlinguae, maxillae, and labium. 



Korschelt and Heider (1898) also, in their text-book quote 

 Metschnikoff and vom Rath, and allude to the necessity for 

 further investigation into this matter. 



Heymons (1897), in an account of the embryo of Glomeris, 

 states very decidedly that its gnathochilarium is formed of 

 only one pair of appendages and the hypopharynx (hypo- 

 stome), but ventures no surmises as to the origin of the 

 hypostome. 



Silvestri (1898), in describing the larva of Pachyulus 

 communis says that though there is only one pair of 

 appendages in the gnathochilarium yet two sterna are also 

 concerned in its formation ; namely, the sternum of the 

 maxillary segment and that of the post-maxillary segment, 

 and that it is this latter sternum which corresponds with the 

 hypostome of Latzel. This implies the existence of two 

 maxillary segments, though one of them is without appendages. 



The fact that only two jaw-bearing segments were known 

 in Diplopods was one of several reasons given by Professor 

 Lankester (1903), for placing the Diplopods (Dignatha 



