NO. 10 CRUSTACEAN METAMORPHOSES SNODGRASS 3I 



large second maxillae (C, 2Mx) are much thickened and securely 

 grasp the base of the attachment filament (/) by means of hooks 

 imbedded in apical depressions. Then the larva backs away and draws 

 the filament out to its full length, and thus maintains its hold on the 

 gill with sufficient freedom of movement for feeding. At the next 

 moult the sexes are mature. The female grows to a length of 4 or 

 5 mm., but the male remains a pygmy not over i mm. long. 



In the adult female (fig. 11 E) the maxillae are greatly lengthened, 

 but the filament (/) is contracted so that only a short stalk projects 

 beyond the maxillae. The maxillae of the male (D) are relatively 

 not so long as those of the female, but the filament is unshortened. 

 The filament, being a product of an internal head gland, is not shed 

 and renewed at the moults ; it retains its attachment and thus allows 

 the parasite to complete its life in security within the gill chamber 

 of the fish. The long filament of the small adult male permits the 

 male to swing around on his tether until he comes in contact with a 

 female, whom he grasps with his maxilliped claws and then lets go his 

 hold on the filament, which remains attached to the gill. The female 

 of another similar species of the genus Salminicola (F) is depicted 

 by Wilson (1915) carrying her extruded eggs {es) in two long 

 cylindrical sacs projecting from the gonopores while still attached to 

 the gill of the fish. The newly hatched young presumably are carried 

 out of the gill chamber in the expiratory currents of water. 



A good example of a parasitic copepod that inhabits two hosts dur- 

 ing its life is the well-known fish parasite Lernaeocera branchialis 

 (L.), a member of the Lernaeopodidae. This species during its larval 

 life is an attached parasite on the gills of a flounder, but when adult 

 both the male and the female become free and leave the flounder. The 

 male undergoes no further transformation, and, after mating with a 

 female still on the flounder, his purpose is accomplished. The female, 

 on the other hand, is not yet sexually mature, and some instinct now 

 urges her to leave the flounder and to seek a cod on which to com- 

 plete the development of her ovaries. Once attached in the gill 

 chamber of a cod she goes through an adult metamorphosis by which 

 she is functionally reduced to the bare essentials necessary for feeding 

 and egg production. For an account of the life history of Lernaeocera 

 hranchialis we may draw on the work of Pedaschenko (1898), Scott 

 (1901), Wilson (1917), Schuurmans-Stekhovcn (1936), Sproston 

 (1942), and Capart (1948). 



There is some difference of opinion concerning the nature of the 

 early forms of this species. Pedaschenko says the first larva is a 

 metanauplius (fig. 12 B) ; Scott and Sproston observed only one early 



