180 



SCIENCE-GOSSIP. 



[August 1, 1866. 



arriving here in a clean state, from sandy bottoms in 

 deep water, do not long keep clean, however ; for 

 remain sluggishly as much as they will in the 

 shadows of overhanging rockwork, their pale buff 

 colour becomes gradually green, which darkens as* 

 the carapace gets farther covered with a velvety coat 

 of algse. Some of our Hyas have, in addition, num- 

 bers of a small simple (i. e. not compound) ascidian 

 {Cynthia) growing on them, and others have their 

 limbs quite covered with an encrusting Polyzoa. 

 But I have never known any red, or much less any 

 brown algse spring up on Crustacea in aquaria. Nor 

 are active crabs, whether they are occasional bur- 

 rowers or not, such as, e.g., the common shore 

 crab {Carcinus mams), or the various swimming 

 crabs, as Portunus and Portumnus ; nor are es- 

 sentially burrowing crabs, however slow they 

 may be, for example, Ebalia, Gonoplax, and Co- 

 rystes, liable to become thus covered with weeds 

 or other parasites, whether in the sea or in cap- 

 tivity, unless in the latter case they are cruelly 

 deprived of sand or other substances to burrow 

 in, and are otherwise hindered from getting 

 into dark places. Some years ago, a lobster 

 (Eomarus) was kept in one of the smaller central 

 tanks of the Regent's Park aquarium, where it had 

 no opportunity of hiding, and it became covered 

 with quite a forest of green seaweed {Enteromorpha) . 

 Here the same species is similarly grown over, 

 especially in summer, but to a very much smaller 

 extent, as in our aquarium there are many hiding- 

 places. But our spiny lobsters {Palinurus quadri- 

 cornis) being of less hiding habits than Homarus, 

 become rather more densely invested with plants in 

 warm weather. These specimens of Palinurus 

 when they first came from the sea, were thickly 

 covered with thousands of a little living tubicolous 

 annelid {Spirorbis communis), the rough carapaces 

 and the prickly peduncles of the great external 

 antennae of the lobsters forming suitable surfaces 

 for the attachment of the shells of these worms, 

 which have multiplied in the aquarium till they have 

 become quite a nuisance, as they have cemented 

 themselves not only to rough surfaces of the rock- 

 work and slate of the tanks, but also to their glass 

 fronts by hundreds, and have to be scraped off with 

 a steel instrument. One female Palinurus is loaded 

 with eggs, which she carries below the abdomen, 

 with the tail closely doubled under, so as to keep the 

 spawn in a kind of pocket thus formed. In this 

 state she is not so active as her fellows, and she is 

 placed in a separate tank, so as not to be disturbed 

 by them ; and as a consequence of her slowness she 

 has become grown over on various parts of the 

 lower surface of her shell with a great family of 

 living branching Polyzoa. Trifling as is the motion 

 of the creature in her present condition, it may be 

 enough to imitate the waving motion of the sea, in 

 a greater degree than is given by the current of 



water which usually flows through the tank, while 

 the roughness and darkness of the lower half of the 

 animal's crustaceous covering may supply the other 

 conditions necessary for the well-being of this kind 

 of Polyzoa, so seldom kept in aquaria alive. 



Slowly moving Crustaceans, however, are not the 

 only animals on the shells of which live other 

 animals and various forms of vegetation. The 

 periwinkle {Littorina), for example, is often found 

 with fucus (Tang) growing upon it, this plant in- 

 habiting the zone of extreme high water, in which 

 the mollusc also lives. But no mollusc with which 

 I am acquainted is so interesting in this respect as 

 the very slow and very rough rock-winkle {Murex 

 erinaceus), when dredged up in Weymouth Bay, in 

 Dorsetshire. Most of the specimens from this 

 locality have attached to them beautiful little 

 healthy fronds of Rhodymenia, Iridcea, Chondrus, 

 Phyllophora, and other red algse, in fine condition, 

 and well adapted from their small size for aquarium 

 purposes. I often obtain them, hoping that the 

 habits of the Murex will carry the weed, into dark 

 corners of the tanks, where the plants will continue 

 to flourish. But after a time they become covered 

 with dirty-looking'confervse, and lose their freshness 

 of appearance, like all other red algre in captivity 

 and in too much light. The successful aquarium 

 cultivation of Rhodosperms free from confervse, 

 and under circumstances enabling these plants 

 to be readily seen in the very subdued light they 

 require, is a thing to be yet learnt. But I some- 



,., . 



Fig. 166. The Spider-Crab (Hyas araneus). 



times by chance manage them very well. Last 

 week (April 2Sth), for instance, I had occasion 

 to examine the state of our two marine filters, 

 which are a pair of slate tanks, seven feet long, and 

 three feet broad and deep, closely covered over with 

 wooden flaps, so that the insides of the vessels are 

 always . in total darkness. They are filled to within 

 about six inches of then tops with fine sand, through 

 which constantly flow strong currents of sea-water. 

 Into these filters I from time to time throw surplus 



