HALICHONDRIA. 95 



Sponge arbuscular, erect, from G to 10 inches in height ; the 

 stalk compact, hard, cylindrical and usually short, dividing in a 

 sub-dichotomous manner into numerous unequal branches, which 

 often inosculate or are connected by lateral shoots ; they are 

 roundish, obtuse, of a straw-yellow colour, smooth, soft, and 

 woolly to the touch, elastic, of a fibro-reticular texture, the 

 fibi'e slender, smooth and translucid, radiating from the centre 

 upwards and outwards, and foraiing by its inosculations tetra- 

 gonal or pentagonal meshes, so small as scarcely to be visible 

 with the naked eye : fecal orifices rather small, generally not 

 numerous, mostly disposed along the margins, but a few are 

 often scattered over the surface, especially where the branches 

 divide. The spicula are short, stout, cylindrical, with acute 

 ends, which are both alike. 



The remarkable specimen represented in our plate was found 

 in the Frith of Forth, and presented to me by my friend Dr P. 

 W. Maclagan. It grows from the back of a small crab (Hyas 

 aranea), — a burden apparently as disproportionate as was that 

 of Atlas', — and yet the creature has been seemingly little in- 

 convenienced with its arboreous excrescence, for it is big witli 

 spawn in a state nearly ready for laying ! Indeed the protection 

 and safety which the crab would derive from the sponge might 

 more than compensate the hindrance this opposed to its free- 

 dom and activity. When at rest its prey might seek without 

 suspicion the shelter afforded amid the thick branches of the 

 sponge, and become easy captives; — while when in motion scarce 

 an enemy could recognise it under such a guise, and the bold- 

 est might be startled at the sight of such a monster : 



— — — — " nicthought, 

 The wood began to move !" 



The Spongia dichotoma of Esper, Spong. pi. 4, fig. 1, 2, which 

 is made a variety of this species by Lamarck, appears to us to 

 be distinct. 



