Salt Marshes and their Inhabitants. - 29 



an unnecessary degree of mystery." A very simple observa- 

 tion would nave shown Dr. Hassell that these motions take 

 place naturally during the growth of the plant, and while it is 

 free from any of those disturbing causes alluded to. Indeed, 

 it is by these motions only that we can explain the very rapid 

 spreading of the filaments over a large surface, which pheno- 

 menon may be easily witnessed both under natural and 

 artificial conditions. 



The oscillation is seen even more beautifully in a nearly 

 allied genus, Spirulina, which may occasionally be found 

 spreading over decaying leaves and other organic matters in 

 brackish water, or in the sea near high- water mark. The 

 plant itself is also much more elegant than Oscillatoria, con- 

 sisting of a slender filament, twisted closely upon itself so as to 

 resemble a very delicately threaded screw of a beautifully 

 delicate green tint. Another very curious organism of- the 

 same group, and occurring also, though much more rarely, in 

 salt marshes, is Microcoleus anguiformis, which may be described 

 as consisting of a number of short threads of an Oscillatoria 

 packed together into a bundle and enclosed in a tubular sheath, 

 wide and open at one extremity, pointed and closed at the 

 other. Out of the open extremity the threads protrude and 

 oscillate, or they may even exhibit themselves from a rent in 

 the side of the sheath. 



If we scan closely the bottom of one of the black unin- 

 viting pools before-mentioned, we shall probably find that it is' 

 marked in patches, or it may be all over, with small closely-set 

 holes, each of which opens at the apex of a slight eminence. 

 The tubes with which these perforations communicate are, in 

 fact, the habitations of a curious Amphipodous crustacean 

 (Corophium longioorne), but whether they are really the work 

 of the Corophium, or are merely taken possession of by the 

 creature, as a hermit-crab takes possession of a deserted 

 shell, is not so easily decided. I believe that the tubes 

 are mostly excavated by a small annelid. At any rate, 

 whole colonies of annelids may often be found inhabiting them. 

 There is no doubt, however, that the Corophium has the power 

 of burrowing very rapidly into soft mud, and it makes use of 

 this faculty whenever it is alarmed and wishes to conceal itself; 

 probably also when pursuing its prey. But though I have 

 kept specimens in confinement for several days I never could 

 find that they formed any regular tubes like those which we see 

 them inhabiting in their natural haunts. There is a traditional 

 enmity between Corophium and the Annelids, and it is quite pos- 

 sible that it may, after killing the architects, take possession of 

 their burrows. So indeed, Pagurus hasbecn said (but not proved) 

 to do with themolluscan builder of its appropriated habitation. 



