146 ANIMAL LIFE 



The performance of work done out in the open 

 leads in each class to a capacity for new response, 

 and therefore to greater variety of handiwork. 



Amongst the Protozoa, those are the most 

 complicated and the highest which have left shelter 

 to inherit the fuller traditions of the open sea. 

 Amongst the zoophytes there is one family — the 

 siphon-bearers — that has surpassed all others in 

 gracefulness and variety of shape, in intensity of 

 colouring and virulence of poison, and it is this family 

 of the blue velella and the violet ' Portuguese man-of- 

 war ' that has had no rest, that has felt the unceasing 

 beat of the sea, and without intermission has been 

 stimulated to action. A more familiar example is 

 the hydroid-polyp of the shore, with its simple struc- 

 ture and plant-like responses, and the jellyfish that 

 arises from it but strikes out to sea, where its eyes 

 and ears, its muscles and poison-organs become elabo- 

 rated through its constant adjustment, varying to 

 meet the changing action of light and waves and 

 the choice of food. 



But it is on land and in air that adjustment be- 

 comes more arduous, oxygen more plentiful, and 

 advance, though difficult, more pronounced. The 

 play of light, heat, and vibration, the influence of 

 weight, the sources of friction, the steepness of hills, 

 all tell witli greater force on land than under water. 

 To those animals that can make the adjustments and 

 endure even for a few months the rigour of a changing 

 climate a higher place is assured than to their brethren 



