z8o CRUSTACEA. 



covered with hydroids and sponges, which settle on the 

 shell. There is no doubt, however, that some actively 

 mask themselves, for besides those known to use the 

 Tunicate cloak, others have been seen planting sea-weeds 

 on their backs. The protective advantage of masking both 

 in offence and defence is very obvious. 



The intelligence of crabs and some of the higher Crus- 

 taceans is well developed. Maternal care is frequent. 

 Fighting is very common. The loss of limbs is readily 

 repaired. 



Deep-sea Crustaceans are very abundant, and often 

 remarkable "for their colossal size, their bizarre forms, and 

 brilliant red colourings " ; some are blind, others are 

 brilliantly phosphorescent. Yet more abundant are the 

 pelagic Crustaceans (especially Entomostraca and Schizo- 

 pods) ; they are often transparent except the eyes, often 

 brightly coloured or phosphorescent. Many Crustaceans 

 live on the shore, and play a notable part in the struggle 

 for existence which is so keen in that densely-crowded 

 region. The lower Crustaceans are abundantly represented 

 in fresh water, in pools, streams, and lakes. A few, such as 

 wood-lice and land-crabs, are terrestrial, and some blind 

 forms occur in caves. 



