1 66 THE BIOLOGY OF THE SEA-SHORE 



weed, algal spores, etc., which provides rich nutriment for 

 those forms which are able to extract it. Since the object of 

 burrowing is predominantly concealment, Eisig has applied 

 the term " cryptoid " to this form of locomotion. He 

 further recognises three or four subdivisions according as 

 to whether the chief agent in burrowing is the proboscis 

 {e.g. Glycera) or the paropodia {e.g. Aphrodite, Psammolyce, 

 etc.), or whether the initial movement is one of swimming 

 {e.g. Nephthys, Sthenelais) or a screw-like (helicoidal) motion 

 {e.g. Lumbriconereis). 



Another group in which the burrowing habit is exceed- 

 ingly well developed is that of the Crustacea. In some 

 forms the burrowing is only very superficial and temporary 

 (prawns and shrimps) ; others, particularly tropical amphi- 

 bious forms, excavate galleries in mud and sandbanks which 

 are practically permanent. Between these two extremes are 

 numerous forms which excavate temporary burrows that 

 are destroyed at each new tide, e.g. the common sand-hopper. 

 Many interesting accounts have been given of the habits of 

 the burrowing Crustacea of American shores, but it is only 

 possible to accord them the briefest mention here. The 

 method of burrowing of the American " fiddler " crab 

 {Gelasimus pugilator) has been observed by Verrill and 

 Smith (quoted by Stebbing, 1893). The holes made by 

 this species are mostly from half an inch to an inch in 

 diameter and a foot or more in depth, the upper part nearly 

 perpendicular, becoming horizontal below, with a chamber 

 at the end. The moist sand is removed in small pellets, 

 the crab transporting each pellet to a distance of four or five 

 feet from the hole before depositing it and running quickly 

 back for a new load. Another writer, Smallwood (1903), 

 has made a number of interesting observations on the habits 

 of the American " beach-flea " {Talorchestia longicornis). 

 The burrows, from 4 to 20 cms. deep, of this species may 

 occur over an area extending from a short distance below 

 ordinary high-tide mark to a little above the spring-tide line, 

 and are temporary. The animal rests in a small chamber at 

 the lower end, always in damp sand, and the hole is usually 



