RESPIRATION IN SHORE ANIMALS 213 



specialisation, however, is seen in the " masked crab " 

 {Corystes cassivelminus), although this is not, strictly speaking, 

 a shore species. The antennae of Corystes, unlike those of 

 the majority of crabs, are very long and are fringed with 

 hairs arranged so as to interlock when the two antennae 

 are apposed, and to form a long tube. When the crab 

 burrows, the tips of the antennae are left protruding at the 

 surface and, by a reversal of the normal respiratory current, 

 a stream of water is kept passing down the tube into the front 

 ends of the gill-chambers. At the entrance to each gill- 

 chamber is a hairy filter which rejects any particles of mud 

 that may have entered the tube with the water (see Garstang, 

 1896, and Zimmermann, 19 12). The reversal of the 

 normal respiratory current and the formation of an antennal 

 tube, along with other slighter modifications, constitute a 

 remarkable adaptation to the burrowing habit. 



Respiration in Relation to the Turbidity of Inshore 

 Waters. — Shore waters are always more or less turbid 

 owing to the stirring-up by wave action of the sand and 

 mud of the sea-bottom. In addition, a large amount of 

 silt is continually being brought down by rivers. Such 

 considerations naturally prompt us to inquire whether 

 turbidity is a factor of any importance in the life of shore 

 animals and, if so, what is the manner of its action ? It so 

 happens that there is not a little evidence, some of it of more 

 than usual weight, to show that the presence of a quantity 

 of solid particles in suspension does actually present an 

 important problem to certain members of the shore fauna, 

 and this is mainly because of their tendency to impede the 

 proper functioning of the breathing organs. The problem, 

 in fact, is closely analogous to that affecting burrowing forms 

 which have to find some means of obtaining their water of 

 respiration free of sand particles. Moreover, in both cases 

 the most important adaptive modifications are observable 

 among the higher Crustacea. Zimmermann (19 13) remarks 

 *' on a praiseworthy striving after cleanliness " on the part 

 of the Galatheidas, and instances numerous ways in which 

 the members of this group {e.g. Galathea squamifera, Porcellanq 



