THE COPEPODA 



of origin is indicated by the possession of a larval glandular organ 

 of adhesion in the frontal region (Fig. 45, A, f.gl). In the 

 Caligidae the first Copepodid stage becomes attached to the skin of 

 a fish by a long filament (frontal band) which appears to be formed 

 by the consolidated secretion of a convoluted tubular gland lying 

 in the frontal region. Larvae in this stage were described by 

 Burmeister as a distinct genus, under the name Chalimus, and it 

 may conveniently be designated the Chalimus-st&ge. In later 

 stages both sexes become free, and in some species at least 

 retain the power of swimming freely, attaching themselves only 

 temporarily to fishes for the purpose of sucking their blood. 

 The males and females, at the stage at which fertilisation takes 

 place, do not differ greatly, but after impregnation the genital 

 somite of the female becomes greatly distended and filiform egg- 

 masses are produced. 



A more complex life-history is that of the Lernaeidae. Lernaea 

 branchialis is hatched as a nauplius, and when it reaches a stage 

 corresponding to the first Copepodid stage (Fig.- 51, A) it becomes 

 parasitic on the gill-filaments of 

 a fish, usually one of the Pleuro- 

 nectidae, attaching itself at first 

 by the subchelate antennae and 

 the maxillae, and later by the 

 frontal cement-gland. It then 

 passes into a " pupal " stage 

 (Fig. 51, B), in which the power 

 of movement is lost and retro- 

 gressive changes occur, especially 

 in the swimming - legs, which 

 lose their setae and become 

 unsegmented stumps. Later, 

 the power of locomotion is 

 regained, and the parasite leaves 

 its first host in a form which 

 corresponds to the adult stage 

 of free-living Copepods. Sexual 

 maturity is now reached and 

 the female (Fig. 52, B) is dis- 

 tinguished by the great elonga- 

 tion of the region of the genital 



Segment. Impregnation takes produced by frontal gland ; oc, nauplius-eye. 

 ,, r (After Clans, from Korschelt and Heider's 



place in this free -swimming Embryology.) 



stage and the mule does not 



develop further. The female, however, seeks a second host, a 



fish of the family Gadidae, and becoming attached to the gills, 



burrows into the flesh so that the whole anterior region of the 



Fio. 51. 



