August 1, 1S66.J 



SCIENCE-GOSSIP. 



179 



fuci,* so that they are sometimes completely covered 

 by a mass of these marine plants growing upon 

 their surface, 'where their roots find a secure hold 

 amongst the villous coat of the shell and limbs. 

 Say supposes that the fuci which are found 

 covering certain Crustacea, are merely entangled 

 mechanically in the hooked hairs by which they are 

 covered, but there is no doubt that they actually 

 grow upon them and are attached by roots. This 

 is evident from the healthy state of the little plants, 

 as well as from the direction of the branches." Mr. 

 Bell also alludes to various kinds of vegetable 

 and other growths covering other spider-crab s 

 {Stenorhynchus, page 5 ; Iiiachus, page 17 ; Pisa 

 Gibbsii, page 28 ; and Hyas, pp. 33, 31). My own 

 experiences in these matters coincide with Mi\ 

 Bell's. Thus I have often had brought me living 

 specimens of the spinous spider - crab (Maia 

 Squinado), sometimes without any seaweeds on it, 



Fig. 165. Four-horned Spider-Crab (Pisa tetraodon). 



and sometimes quite covered with such algae as 

 Gracilaria, Hypnea, Gelidium, Gymnogongrus, Fur- 

 cellaria, Polyides, and other seaweeds having 

 thread-like or stiff wire-like fronds ; so that when 

 they were washed about horizontally by the sea, 

 their filiform character caused them to become 

 entangled in a complicated manner in the strongly 

 hooked hairs with which Maia is beset, and the 

 weeds could be " drawn out of the hooks " as Mr. 

 Jesse describes, but the plants were always attached 

 fast to the crab shell by their roots also. No spider- 

 crab known to me can cut up algae into strips, nor 

 yet attach such strips to its carapace, at any rate 

 not to its upper portion, for the most they can do 



* The word "fuci," as employed in these two instances, 

 is not intended to convey the idea that actual fucaceee are the 

 plants attached to the crabs. Mr. Bell uses it, as did many 

 of the older naturalists, whose general name for nearly all 

 the Rhudosperms was Fucits, in the same manner that they 

 applied the term ''Cancer 7 ' to almost all crabs, and Actinia 

 to all sea-anemones. 



in this way is to use their limbs to "preen" them- 

 selves with a little, but always in a very feeble and 

 awkward manner. 



Hyas ara/ieus is a spider-crab which I get with a 

 perfectly clean shell when brought up from deep 

 water on a clean sandy bottom, on the coasts of 

 Essex and Kent, and off the island of Heligoland ; 

 but when it comes closer in shore and hides among 

 weed-covered ledges of rocks, then these crabs are 

 frequently covered with dense bushes of red algae 

 (Ehodospermce), and, in explanation of why these 

 plants are red, and not brown (JSIelanospermce), or 

 green (Chlorospermm) — marine algae being thus 

 systematically divided into these three great classes 

 by their colour — it has to be stated that the red 

 algae grow in shady places, and when found be- 

 tween tide-marks, they are generally met with con- 

 cealed under a curtain of green and brown weeds, 

 which prefer the light. Consequently, as the hiding 

 habits of the crabs cause them to inhabit the same 

 localities as the red weeds, it is natural that the 

 latter should grow on the animals, especially as 

 their rough and hairy shells and slow motion 

 are well adapted for the purpose. But when 

 the red algae, whether living on a crab or any 

 other object, are found in a place where the shadow 

 is inconsiderable, as, for example, on the sea- 

 shore, very high up between tide -marks, or in 

 an aquarium, where the light is greater and the 

 temperature higher than in the sea, then the red 

 weed loses its colour, becomes lighter in hue, gets 

 deteriorated, and becomes gradually overgrown with 

 parasitic confervae. About twelve years ago, Mr. 

 Robert TTarington published in the Zoologist an 

 account of some interesting experiments made by 

 him, in which he showed how he restored to their 

 normal condition, some Bhodosperms, which had be- 

 come overgrown with confervae, by placing them in 

 variously coloured glass jars, which permitted the 

 growth of one kind of alga, but not the other. 



In the Hamburg Aquarium (tank No. 10) are two 

 large spinous spider-crabs (Maia Squinado), which 

 arrived from the coast of Erance, Yuiite free from 

 any algae. After they had been here for some weeks 

 their shells began to be rapidly grown over by green 

 alga3, and this had to be removed with much diffi- 

 culty, by hand. In one corner of the tank is a large 

 and perfectly dark cave, formerly inhabited by a 

 pugnaciously disposed lobster {Horn ants vulgaris), 

 who would not allow the spider-crabs to enter its 

 den. But I removed the lobster, and the crabs im- 

 mediately took possession of the cave, and now, as 

 they pass much of their time in darkness, the algae 

 have ceased to grow upon them, save to a small 

 extent. The under parts, however, of these slow 

 crabs being ever in almost absolute darkness, have 

 become covered with patches of a compound ascidian, 

 Botryllus polycyclus, a creature fond of shade. 



The specimens of Hyas, which I have named as 



