a Family of Thysanura. 367 
dure never belong to the last ring, but take their rise from the 
= ventral shield of one of the preceding rings, both when they 
preserve their original plain form and when they are transformed 
into a springing-apparatus. 
Neither in Japyz nor in any species of Campodea have I been 
able to discover eyes, though both Guérin and Nicolet assert 
that they have found eyes in the species of Campodea examined 
by them. 
Japyx, Hal. 
Cerci breves, inarticulati, cornei, forcipis instar. 
Segmentum ultimum maximum, pznultimum breve, scuto 
ventrali fisso. 
Mandibule paululum compressz, serrate. 
Mala interior maxille lobis quinque laciniatis instructa. 
Palpi maxillares biarticulati. 
Labium verrucis (palpariis?) duabus anticis permagnis in- 
structum. 
Palpi labiales conici, setis simplicibus muniti. 
Antenne setacez, articulo ultimo parvo, minore quam pen- 
ultimo, conico. 
Oculi nulli. 
- Unguiculi simplices, ineequales, onychio unguliformi. 
Spiracula dena. 
The following description of the mouth in this genus applies 
in all essential respects to the whole order of Thysanura gene- 
rally :— 
The mandibles (fig. 1 a) are elongated, flat, and their basal part 
attenuated into a point without any vestige of condyles. The 
_ proportion of their breadth to their length is as 1 to 6 or 7, 
and they are therefore comparatively much more robust than 
those of Antliata and Rhynchota, which are setiform or subuli-. 
form. But the principal peculiarity of the mandibles in Japyx 
and other Thysanura is that they are hollow, and that their great 
flexors (c) penetrate into their interior through a longitudinal slit 
or fissure along their inward edge, and fix themselves inside the 
mandible on the wall of the cavity opposite the fissure; whilst 
in other insects the mandibles are solid, and the muscles.are all 
fixed to their outside by tendons. The opposite ends of the 
flexors of the mandibles, as well as of their tensors, in Japyx 
are attached to a chitinous plate (fig. 1 b) situated between the 
mandibles, and steadied by a double set of muscles (fig. 1 g h). 
_ Thus the mandibles can be approached to one another; but, in 
order to give this movement sufficient precision and strength, 
the mandibles must turn round some firm centre of movement ; 
and as they do not articulate with the skull as free biting 
