24 BRITISH PARASITIC COPEPODA. 



phtheirus and allied forms are not parasites in the strict 

 sense of the term, and may not be hurtful to their 

 hosts. There is little doubt about the food of Lernsea. 

 It is generally found in a position that is plentifully 

 supplied with blood. Its mouth is buried out of the 

 reach of mucus, and is often in direct communication 

 with the main blood- stream entering the gills to be 

 purified. Caligoids from the gill-chamber and the 

 mouth seldom show any trace of red colour. Degene- 

 rate forms such as Glavella and Chondracanthus, 

 although actually living amongst the gill-filaments, 

 are usually of a pale yellow colour, with occasionally a 

 grey central streak indicating the alimentary canal. 

 Lernanthropus Jcroyeri, which lives amongst the gill- 

 filaments of Labrax lupus, is nearly always of a deep 

 brownish-red colour. It is said that mucus at the best 

 is a poor food, but Lepeophtheirns can live for upwards 

 of six weeks in filtered sea- water without visible food 

 of any kind. Mucus may not be a very sustaining form 

 of nourishment, but as the Caligoids apparently do not 

 require much food they may be able to obtain sufficient 

 from the mucus. C. B. Wilson says : " There is more 

 mucus on the scales than anywhere else ; why should 

 they choose the fins or inside of the operculum? " The 

 fins and gill-chamber afford a certain amount of pro- 

 tection to the parasites, and it is just as likely that 

 they choose these places for shelter as for food. It 

 has to be remembered, however, that the difference 

 between the Caligoida and the obviously blood-sucking 

 Lernsea is very great. The Caligoids are provided 

 with large digestive glands which are entirely absent 

 in the adult female Lcrnwu. When one finds blood in 

 the alimentary canal of a parasite which has no digestive 

 glands, and none in those which are provided with 



