THE MOVEMENTS OF SHORE ANIMALS 159 



with shore fishes is the tendency shown by certain species 

 of blenny to leave the water for short periods to clamber 

 over the rocks in order to bask in the sun. For this purpose 

 the pectoral and pelvic fins are employed, in both of which 

 the fin-rays are firm and fleshy. In point of fact the ventral 

 fin on each side is reduced to a couple of stout processes 

 resembling fingers. 



Any adaptation of particular interest noticed in a shore 

 form in temperate regions invariably occurs in more intense 

 fashion among equivalent species in the tropics. Thus 

 Alcock {op. cit.) has observed the behaviour of Gobies of 

 the genera Periophthalmiis and Boleophthalmiis which frequent 

 the mangrove swamps and muddy shores of the Indo- 

 Pacific. During the daytime these fish may be seen basking 

 in the sun, or hunting for food, " raising themselves on their 

 fleshy pectoral fins, as a man, whose legs are paralysed, 

 might use his arms. When pursued, they take great springs, 

 using their tails and ventral fins for the purpose ; and if 

 they cannot escape into the sea, they will dive down a crab's 

 burrow, or dash into a bunch of mangrove roots." Like 

 the British " shanny," these tropical gobies are exceedingly 

 wary when out of the water, having, as Alcock remarks, 

 ** eyes like swivels " (see Fig. 14, p. 207). 



Gliding. — Many shore forms progress by a smooth con- 

 tinuous form of movement in which the lower surface or 

 special organ of locomotion remains in close contact with the 

 substratum, e.g. anemones, Turbellarian worms, Gasteropod 

 molluscs. This form of locomotion is best described as 

 gliding. It is employed in the first place by anemones, 

 several species of which are capable of not inconsiderable 

 displacements. According to McClendron (1906), who has 

 carried out observations on Metridiiim marginatum, the 

 method of progression is similar to the ordinary creeping 

 of a snail ; a.succession of waves travels from behind forward, 

 but in the anemone the waves are larger and not so rapid 

 or regular. The undulations of the foot progress in the 

 direction of locomotion. The functionally posterior foot lets 

 go at several points and slips forward and this contraction 



