STRUCTURE OF THE MALLOPHAGA. 167 



merging gradually into the pigmented optic nerve {oji.). Each eye 

 is directly innervated from the precesophageal ganglion. The 

 hypodermal cells are interposed between the lens and the retinal- 

 cells, as cubic cells in old specimens, but as a hyaline body 

 consisting of cylindrical cells in young or recently-moulted spe- 

 cimens. There are no rhabdites in the eyes. The eyes of 

 Mallophaga resemble those of Phryganea grandis, as described 

 by Grenacher. 



EXPLANATION OF PLATE XX. 



Fig. 1. — Ventral view of head of Lcemobothrium, from Gypogeranus 

 serpentarius, x 30. 



2. — Median section through head of Goniodes dissimilis, x GO. 



3. — Labrum of Goniodes dissimilis, x 60. 



4. — Right and left Mandibles of Tetrophthcdmns, x 60. 



5. — Head of Lipeurus heterographus, seen from below, x 60. 



6. — First maxillae of TetrophtJialmus, x 75. 



7. — Second maxillae of Nirmus, x 60. 



8. — Second m.six\l\8& oi Tetro2Jhthal?nus Chilensis, x 60. 



9. — Second maxillae of Lcemobothrium, x 60. 



10. — Eye of Lcemobothrium, seen on cross-section of the head, 

 X 190. 



Explanation of reference letters in the figures : — 



at, antennae ; ch., chitinous bar ; d.s., v.s., dorsal and ventral 

 parts of oesophageal sclerites ; g., glossa (ligula) ; g.s., 

 glassy body; h. hypodermis ; hy., hypopharynx ; i.s., o.s., 

 inner and outer side of maxilla ; I., lens-shaped chitinous 

 thickening ; lb., labrum (upper lip) ; l.md., r.md., left and 

 right mandibles ; l.jy., labial palp ; m. , muscle ; rnd., man- 

 dible ; mt., mentum ; mx.% first maxilke ; mx.-, second 

 maxillae (labium, or under lip) ; oc. , eyes ; oes. , oesophagus ; 

 o.n., optic nerve ; p., paraglossa ; r., retinal cells. 



