328 '' NOTES. 



" In the young cells, whose partitions, although thin, have already acquired a stony 

 consistence, the exterior surface is quite convex, and the margin of their aper- 

 tures jut out so that they are easily distinguished ; but by the progress of age 

 their appearance changes ; their free surface rises so as to efface the deep de- 

 pressions which marked originally their respective limits, and to raise to the le- 

 vel of the surface the border of the openings. The result of this is that 

 the cells cease to be distinct, or even distinguishable without, and that the poly- 

 pidom seems to be formed of a stony continuous mass, in the substance of which 

 are excavated certain holes slightly widened interiorly, and disposed in quincunx. 



"But differences of this nature cannot be formed by the simple juxtaposition 

 of new calcareous layers under those primitively formed ; for the soft parts of 

 the animal, the only ones which can be the seat of a secretion of this calcareous 

 matter, do not extend over the surface which is thus modified ; and the position 

 of the cells thus immersed in the apparently common mass of the polypidom is 

 often such that we cannot attribute their change of form to any operation or 

 friction of foreign bodies. 



" It appears evident to us that these facts indicate the presence of life in the 

 substance which composes the parietes of these cells, and can only be explain- 

 ed by the existence of a nutritive movement ; like to that which, in the confi- 

 guration of bones, effects analogous modifications. 



" To know better the nature of these cells, I submitted to the action of ni- 

 trous acid diluted with water, a part of a polypidom recently taken from 

 the sea. A brisk effervescence was visible immediately, and in some minutes the 

 cells became flexible, and separated from one another. Before treating them thus, 

 no distinct membrane was seen on the internal wall of these cells ; and when 

 the nitrous acid had destroyed all the calcareous carbonate on which their ri- 

 gidity depended, these same parietes still existed and had not changed their 

 form much : only they were formed now of a soft and thick membrane con- 

 stituting a bag, in the interior of which we perceived the digestive apparatus of 

 the polype. The opening of this bag was no longer truncated, as it appeared 

 when the texture of the membrane was thickened by the stony deposit from 

 which we had just freed it, but the membrane was continued uninterruptedly 

 with the tentacular sheath. 



*' We see then that in the Eschares, the cell in which it is said the polype 

 retires as into a shell, is a component part of the animal itself, in which it conceals 

 itself, if we may use the comparison, as the hedgehog enters into the thorny skin 

 of his back. It is not a calcareous crust which is moulded on the surface of 

 its body, but a portion of the general tegumental membrane, — of the skin of 

 the polype, — which, by a molecular deposit of earthy matter in the meshes of 

 its tissue, ossifies as the cartilages of superior animals ossify, without ceasing to 

 be the seat of a nutritive movement. 



" We see also that that which is considered generally, as being the body of these 

 polypes, constitutes in reality only a small portion of it, and consists of little but 

 the digestive, and probably breathing organs, of these little animals. 



" The tegumental bag, freed from its carbonate of lime, seems to me formed 

 of a toraentose membrane covered, particularly \vithout, with a multitude of cy- 

 lindrical filaments, disposed perpendicularly to the surface, and pressed close to 

 one another. It is in the spaces left between these fibres that the calcareous 

 matter appears to be principally deposited, for if we examine, with the micro- 



