74 CRUSTACEA——COPEPODA CHAP. 
The females carry two long egg-sacs; the general structure may 
be made out from the ventral view of Caligus nanus (Fig. 43). 
Some of the Caligidae are distinguished by the terga of the 
thoracic segments being expanded to form large chitinous elytra, 
e.g. Cecrops, found parasitic on the gills of the Tunny and on the 
Sun-fish (Orthagoriscus mola). Caligus rapax is parasitic on the 
skin and in the gills of Sea-Trout, Pollan, ete.; and C. lacustris is 
common in fresh-water lakes and streams on Pike and Carp. 
Fie. 43.—COaligus nanus, x 10. Abd.1, Fic. 44.—LZernaea branchialis from 
1st abdominal segment ; Ant./, Ant. 2, the Haddock, ¢, x 1. Ceph, 
Ist and 2nd antennae ; Mu.1, Mz.2, cephalothorax ; és, egg - sacs. 
Ist and 2nd maxillae ; Map, maxilli- (After Scott. ) 
pede ; s, siphon; 7.2, Th.5 1st and 
5th thoracic appendages. (After Ger- 
staecker. ) 
Fam. 11. Lernaeidae—These parasites burrow with their 
heads deep into the skin, or even into the blood-vessels or body- 
cavity, of various marine fish. The body of the adult female 
Lernaea is extraordinarily deformed, consisting of a mere shape- 
less sac with irregular branched processes on the head, and two 
egg-sacs attached behind (Fig. 44).  Pennella sagitta* bores so 
deeply into the flesh of its host, Chironectes marmoratus, that 
only the egg-sacs and some remarkable branchial processes 
attached to its abdomen protrude outside the host to the 
1 The genus Pennella also includes parasites on the whales Hyperoodon and 
Balaenoptera. 
