SEGMENTATION OF THE HEAD OP DIPLOPODA. 617 



The Gnatbocliilarium. 



Silvesfcri (1898) found a post-maxillary^ legless segment in 

 the larva of Pachyulus communis. He expresses the 

 opinion that the sternum of this (post-maxillary) segment corre- 

 sponds with the hypostome of Latzel^ and that therefore the 

 gnathochilarium consists of the sternum and appendages of 

 the maxillary segment together with the sternum of the labial 

 (post-maxillary) segment. 



Further, he says that the dorsal part of this labial (post- 

 maxillary) segment does not join the head at all, but forms a 

 neck joined to the first segment of the body. This last state- 

 ment is fully confirmed by my observations in Spiro- 

 streptus. My reasons for thinking that the sternum of this 

 segment does not form the hypostome are given further on. 



Unfortunately none of the larva3 hatched in the Zoological 

 Gardens lived long enough to enable the actual formation of 

 the gnathochilarium to be worked out. But that is now a 

 matter of comparatively small importance since the real 

 question at issue was not the formation of the lower lip, but 

 the number of maxillary segments present in the Diplopoda. 



When the larval Archispirostreptus leaves the egg 

 the mandibles and the second pair of maxillfB are clearly laid 

 down, as indeed can be seen from PI. 37, fig. 2, which represents 

 an embryo still Avithiu the egg-shell. The first maxillas have 

 disappeared, being by this time completely absorbed by the 

 mandibles. But the gnathochilarium is far from being fully 

 formed, and in this my observations do not agree with those 

 oE vom Rath (1891), who found that the young larvse of the 

 Julidfe and Glomerida) left the egg with mouth parts like 

 those of the adult. 



As the larv£e grew in age and size the maxillas gradually 

 approached each other, and in that which lived longest they 

 touched each other; but as yet they were not fused together, 

 nor could I see that they had fused with any other part of 

 the head, or body (see text-figures 1 — 4). 



