APPENDIX II 309 



Halobates show a degree of adaptation to a marine existence 

 which is extraordinary, being found gliding over the calm 

 seas of the tropics hundreds of miles from land or clinging 

 to any flotsam from which they can obtain food. Their 

 eggs have been picked up attached to the floating feather 

 of a sea-bird (see White, 1883, and Carpenter, 1895). 



From the ecological point of view, insects form an 

 important part of the jetsam associations referred to in 

 Chapter III. In fact, it is the shore jetsam, with its mixed 

 plant and animal constituents, which has been the chief 

 factor in attracting these forms to the sea-shore. Probably, 

 also, the warmth of the decaying weed is a condition which 

 favours the development of the eggs and larvae, particularly 

 those of flies and beetles ; moreover, the larvae will have 

 no difficulty in finding a plentiful supply of decaying plant 

 or animal food. 



One of the most abundant and, at the same time, the 

 most typical of sea-shore insects is the Collembolan 

 Anurida marititna^ a small, blue-black, wingless form, from 

 two to three millimetres in length. It is found on or 

 under stones, crawling on weeds or walking over the 

 surface-film of pools between tide-marks, but never above 

 high-tide mark nor in the Laminarian Zone. A supply 

 of air is retained by its thick coating of hairs sufficient to 

 last it for four or five days under water. The orange- 

 yellow eggs are deposited deep in crevices (Imms, 1906). 

 A related insect with similar appearance and habits is 

 Lipura. 



Quite a number of small species of Collembola (spring- 

 tails) and Thysanura (bristle-tails) frequent the sea-shore 

 in addition to the preceding. The spring-tails have been 

 studied by Davenport (1903), among others, and he describes 

 their reactions to contact, moisture, gravity, and air-currents. 

 Some species go into the sand when the tide rises and come 

 to the surface again to take air when the tide falls. They 

 will run up surfaces in the face of the wind, leaping when the 

 top is reached and so being blown back to the starting- 

 point. A common bristle-tail on British shores is Machilis 

 maritima, which is to be found creeping over the surfaces 

 of rocks or resting on and under stones close to high-tide 

 mark. 



