166 THE STORY OF LIFE IN THE SEAS. 



to be found in the slime which, passing continu- 

 ously over the skin, removes the larvae and the 

 spores before they can secure a firm attachment. 



The Crabs, Lobsters and other Crustaceans 

 free themselves from their skin parasites at ever} 

 moult, but in some of the large, old Lobsters and 

 Crabs that are caught a considerable number oi 

 Worms, Barnacles and weeds are frequently found 

 firmly fixed to the carapace and claws, The 

 Limpets and Winkles of our rock pools are ofter 

 covered with a little forest of Algse. 



The shells of other Molluscs are, however, kept 

 remarkably clean, and the method by which thej 

 destroy the spores, etc. that settle upon them is 

 not yet fully understood. 



One of the most serious of the external para- 

 sites is the Hag-fish. This remarkable animal is 

 eel-like in shape, although very different indeed, 

 anatomically, from all the true Fishes, and buries 

 its head in the skin of the Cod and other Fishes 

 as it feeds upon their flesh. In some cases the 

 whole body of the Hag gets inside the host, and 

 it thus becomes an internal parasite. It causes 

 an immense destruction of valuable food fish ir 

 some districts. 



Closely related to the Hag is the marine 

 Lamprey, which fastens itself to Salmon by its 

 suctorial mouth, causing considerable wounds, 

 This parasite sometimes reaches to a length oi 

 two feet, and is often carried many miles Uf 

 the river by the host to which it is attached. 



Most of the Leeches occur either in fresh-watei 

 or in damp forests and marshy places. There is 

 one, however, named Pcntobdetta, which is found 



