III PODOPLEA—ISOKERANDRIA 75 
exterior. Peroderma cylindricum bores similarly into the flesh 
of the Sardine, and where it is common, inflicts considerable 
damage. The males of these curious animals are of more 
normal structure (Fig. 45). Claus! states that fertilisation 
takes place when both sexes are free-swimming, and of a more 
or less similar structure, and that subsequently the female 
Fic. 45.—Lernaea branchialis, Fic. 46.—Achtheres percarum. A, 2, x 4; B, 
6, x10. Ant.1, Ant.2, 1st 6, x4. Ant.2, 2nd antenna; g, stomach ; 
and 2nd antennae ; Br, brain; Mz.2, 2nd maxilla; Map, maxillipede; ov, 
e, eye 3 g, stomach ; ¢, testis ; ovary ; ovd, oviduct. (After Gerstaecker. ) 
vd, vas deferens; ves. sem, 
vesicula seminalis. (After . 
Claus.) 
becomes fixed to her host and degenerates into the shapeless 
mass shown in Fig. 44. 
Fam. 12. Lernaeopodidae—This family may be illustrated 
by the common gill-parasite of Perch and Trout, known as 
Achtheres percarum. The female (Fig. 46), which is much larger 
than the male, and is not clearly segmented, is attached to the 
host by means of the maxillipedes, which are fused distally into 
a pad armed with chitinous hooks. In the male the maxillipedes 
1 Claus, Schriften d. Gesellsch. Marbury. Suppl. 1868. 
