of Shell-substance hy Hydractinia. 7 



above the otherwise smooth surface of tlie excavation, it does 

 seem (as my friend Mr. Parfitt has sagaciously observed) that 

 these excavations are produced by an " acid or erosive agent" 

 of a chemical rather than of a physical nature, which, not 

 being able to dissolve the silex, thus leaves the grains of 

 sand projecting into the excavation (Parfitt on the boring of 

 Mollusks, &c., Trans. Devon. Assoc, for Advancement of 

 Science, 1871). 



May we not assume, then, that this process is one of animal 

 chemistry like that of digestion (wherein the gastric juice will 

 dissolve calcareous matter, but fails to affect a piece of glass)? — 

 the action in Hydractinia being produced not by cells but by 

 the intercellular sarcode, which, like that of the sponge, can 

 prolong itself into villous pseudopodial processes (fig. 7, c, ^), 

 which possibly may be the pioneers of all vital changes of this 

 kind, in exercising on their confines that catalytic power of 

 which life alone is capable.. 



Indeed Professor Allman has long since demonstrated the 

 existence of sarcode among the Hydroid polypes, which, to use 

 his own words, " comports itself exactly like the pseudopodia 

 of an Amoeba^ which it also resembles in structure" ('Annals,' 

 1864, vol. xiii. p. 204); so that the worm-eaten appearance 

 presented by the lowermost layer of the crust of Hydractinia 

 echinata (that is, in the calcareous surface of the shell just about 

 to become transformed) may be produced, as before stated, by 

 a villous layer of minute pseudopodial prolongations from the 

 coenosarc. 



Lastly, as regards the power of animal chemistry in these 

 operations, which is chemistry directed by an unknown agent, 

 as the production of alcohol by the yeast-plant, &c., it signifies 

 that there is an instinctive power acting here, which is far 

 beyond any possessed by the highest cerebrated being, if I 

 may use the expression. 



When I observe the delicate mycelium of a minute fungus 

 growing or creeping (for the terms are synonymous here) 

 through the hard crystalline layers of the shell of a Buccinum — 

 when I observe on the surface of a lancet which has been care- 

 fully protected by a layer of animal fat a similar kind of my- 

 celium, which has wriggled its way not only over but in the 

 surface of the polished blade by oxidation of the iron in its 

 course, so as to leave a rusty image of itself — and when I ob- 

 serve a plant-like form of glauconite in the substance of an 

 agate which has been formed in a geode of an igneous rock, 

 so much like a Conferva that it might easily pass for one if 

 not otherwise understood, to say notliing of the dendritic 

 markings of rocks, &c., — these facts, taken in connexion, seem 



