I 3 4 THE BOOK OF NATURE STUDY 



esting, and should not be omitted from any marine aquarium. 

 This form reaches a length of 6 or 7 inches, but the aquarium 

 keeper will do well to confine himself to the young, which often 

 swarm in the rock pools in spring and early summer, and with 

 ordinary care will live well. The fifteen-spined stickleback 

 (Gasterosteus spinachia) is readily recognised. The body is elon- 

 gated and slender, and terminates in a small mouth at the end 

 of a long snout. Very characteristic is the way the little creature 

 roots about with this snout in the crevices of the rock pools 

 searching for food in a way which suggests the pipe-fish, which 

 has a somewhat similar habit. The first dorsal fin is represented 

 by fifteen spines, the body is ornamented at each side by strong 

 plates, while the tail fin, that near the anus, and the second dorsal, 

 have all a characteristic fanhke appearance. Like the other 

 sticklebacks, the fifteen-spined form makes a nest, which may 

 sometimes be found in sheltered pools. 



Among other shore fish mention may be made of the flounders 

 and their allies, or flat-fish (Pleuronectidce\ young specimens 

 of which are very common with shrimps in the shallow sandy 

 pools. Young flounders are not very easy to keep alive ; they 

 do best in a wide shallow dish with a thick layer of sand over 

 the bottom. The most interesting point is first the extraordinarily 

 close resemblance in colour between the upper surface of the 

 fish and the sand in which it lives. The same close resemblance 

 is seen in the shrimps, in company of whom the flounders live. 

 Just as the shrimps normally lie half buried in the sand, from 

 which in colour they cannot be distinguished, so the flounder lies 

 normally with only its head protruding, this head looking like 

 a mere elevation of the sand. When the little creature is dis- 

 turbed, however, the silvery colour of the under surface is seen 

 as it glides rapidly away. The next point to be noticed is the 

 curious flattened shape which obviously fits the " flat-fish " for 

 their life on the bottom. Not a few fish are similarly adapted 

 for life on the bottom, the skate and the fishing frog mentioned 

 above are examples. But in these two cases the flat surfaces 

 are, as one would expect, the upper and lower surfaces of the 

 fish, the upper or dorsal having the backbone running down 

 it, and the lower or ventral being that which lodges the heart 



