234 



MYRIOPODA. 



m.t 



mac, 



slightly in different forms. The segmentation is distinguishable not 

 merely, as in earlier stages, on the ventral surface, but is now 

 continued towards the dorsal side (Fig. 118). "When the larva is 

 hatched, its whole body is, as a rule, distinctly segmented (Fig. 

 121 B), though variations occur in this respect. 



The embryonic envelope of the Diplopoda (and of the Myriopoda 

 generally*) is a structureless cuticle secreted by the superficial 

 ectoderm of the embryo. In Julus, its secretion has already 

 taken place before the germ-band shows any signs of segmenta- 

 tion. This membrane which, in its origin, closely resembles the 

 blastodermic cuticle of the Crustacea, forms a sac round the 

 embryo and soon separates somewhat from the surface of the latter. 

 When the germ-band attains its ventral flexure, a corresponding 

 infolding appears in this envelope, which remains somewhat closely 



apposed to the ventral 

 surface. The cuticle is 

 retained during the course 

 of further development, 

 and still surrounds the 

 embryo like a sac when 

 the latter emerges from 

 the egg-shell. The newly- 

 hatched embryo of Julus 

 in consecpuence somewhat 

 resembles a maggot, as 

 is evident from Newport's 

 descriptions and figures. 

 This larva, surrounded by 

 the embryonic envelope, 

 is in a lower stage of 

 development than other 

 newly-hatched Diplopods. 

 The head is not distinctly 

 marked off from the body, 

 nor are the segments fully 

 developed, the germ-band not having fully extended over the dorsal 

 surface. At this stage the larva is still incapable of movement, and 

 may be described as a pupa. Beneath the pupal integument a 



* The embryonic integument of the Chilopoda, according to observation 

 made on Gcophilus, shows the same characters as that of the Diplopoda 



(p. 227). 



OlXj 



Fig. 120. — The gnathochilarium of Lysiopetalum cari- 

 natuui (after O. v. Rath, from Lang's Text-book of 

 Comp. Anat.). mx^, base of the outer and inner 

 ridges (me and mi); mx„, the so-called tongue-plate 

 which carries anteriorly a toothed blade (m); mx 1 and 

 mx„, have been regarded as corresponding to a first 

 and second pair of maxillae. 



