NOTES ON PLYMOUTH SPONGES. 381 



the sponge, an irregular criss-cross, rarely showing well-marked fibres ; 

 looking like a felt of pine-needles, and well represented in Bowerbank's 

 figure (Fig. 300, 3fon., vol. i.). 



This difference is explained when we consider the difference in con- 

 ditions of life : the Exmouth specimen living some fifteen feet below 

 low-water mark, removed from the possibility of any shock or jar ; the 

 Plymouth specimen between tidemarks, exposed to what is often a 

 very violent surf. Such a loose framework as is found in the Exmouth 

 specimen, being very slightly bound together, will dislocate under 

 shocks, and the (sharply pointed) needles drive over one another to 

 form the smaller, and denser, skeleton which is best known to shore- 

 collectors. 



I have found a difference, closely comparable to that between the 

 deep-water Hcdichondria of Exmouth and the surf Halichondria of 

 Plymouth, in Suberites domuncidus. In this species the individuals 

 carried on the back of a hermit-crab have a dense skeleton, like the 

 surf-beaten Hcdichondria, and justify their name with a consistency 

 almost of cork ; while the individuals found growing on rock in the 

 deep waters of Millbay Cliannel (Plymouth Sound) are much larger, 

 supported by a skeleton of precisely similar elements, but much looser, 

 giving the sponge the soft consistency of a ripe plum. 



If the above explanation be correct of the differences between the 

 soft and hard specimens of Suhcrites and HcdicJwnclria, the soft 

 Suberites douiuncidi/s is not a " variety " in the sense that an albino 

 rabbit, or a six-toed cat, is a variety. I am not aware of any word 

 applicable to describe a definite difference from the type, frequently 

 encountered, but known to be due to post-natal influences. It appears 

 useful, in instances where such a history can be proved, to have a word 

 to distinguish the phenomena from those of congenital difference — 

 to distinguish conditional from germinal variation. I suggest the 

 unscholarly, but manageable word, " metamp," suggested by the Greek 

 IJ-erafXTrexoixai = " to put on a different dress." Thus we shall speak of 

 "Suhcrites domunculus met. mollis" ; and distinguish the inherited 

 darkness of the Cinghalese from the metampic brown of the tropical 

 Englishman. Holding, as I do, that the sizes and forms of sponge 

 spicules are largely influenced by the temperature and constitution of 

 the sea in which they grow, I believe that not only varieties, but many 

 so-called species of sponges, are merely metamps of each other. 



To speak of " abnormal forms " does not meet the case — neither the 

 tidal nor the deep-water Hcdichondria can be considered abnormal. 

 The determination of a normal form would, on the view here put 

 forward, mean merely the determination of a normal depth, a normal 

 salinity, or a normal temperature. In the case of littoral and sub- 



