NOTES. 327 



others arc closed, though equally filled with nourishment. The digestion of 

 animal matter is very rapid ; the pachydermatous larva of an insect being ren- 

 dered irrecognisablc in four minutes. Vegetable matter is an inappropriate 

 food, and seemingly indigestible. See Ann. dcs Sciences Nat Part. Zool. tome 

 viii. p. 363, &c — It were well that this anatomy of Corda was confirmed, for 

 the fallacy of the microscope is almost proverbial, and powers of very high in- 

 tensity must have been used in this demonstration. 



4. The nature of the Cells of the Escharidce- Page 238. 



" If the stony cells of the Escharidae were formed by the exudation of a cal- 

 careous matter which moulded itself on the surface of the secreting membrane, it 

 is evident that the first layer thus formed must be the external one, and that the 

 addition of new quantities of this earthy matter could only augment the thickness 

 of the parietes of the cell, and modify the disposition of its interior cavity, with- 

 out at all changing the exterior configuration of the first formed layer ; for here 

 the solid cell completely envelopes the animal, and is not overlapped by the se- 

 creting organ, as in the Mollusca gasteropoda, whose shell changes its form with 

 age, because the deposit of new matter, taking place on the border of the part 

 already consolidated, continually lengthens it, and is moulded on the soft parts 

 whose configuration is liable to change. 



" To throw some light on the mode of formation and on the nature of the 

 cells of the Eschares, it became consequently interesting to examine these cells 

 at diflferent ages, and to see if their exterior form changed or remained always 

 the same. This study, indispensable for the anatomical and physiological history 

 of these little beings, may also lead to a knowledge useful to zoology and to 

 geology J for the determination of the species, recent and fossil, rests principally 

 on the characters furnished by these cells ; and we are still ignorant whether or 

 not they can be modified in the progress of age. 



" This examination can be made more easily than one might at first ima- 

 gine ; for neither the observation of the same individual, at different stages 

 of its developement, nor the collection of a series of specimens so as to repre- 

 sent all the phases through which these little creatures pass successively, is re- 

 quired. Indeed, since these polypes spring from each other, and do not separate 

 from their parents, each polypidom must present a long series of generations en- 

 chained to each other, and in each of these series, the relative age of living in- 

 dividuals must be indicated by the place which they occupy. To resolve the 

 question which we have put, it is sufficient therefore to study comparatively the 

 cells situated near the base of the polypidom, in its middle, in its young branches, 

 and towards the extremity of the latter ; for we are certain that it is not only 

 in this last place that living polypes are found, as some authors affirm, but that 

 they exist over almost the entire extent of the polypidom. 



" After examining in this manner, with a sufficient magnifying power, the cells 

 of the Eschara cervicornis, I am quite convinced that the mode of develope- 

 ment of these stony cells is not that which is usually admitted. 



" Indeed, I have seen that not only does the general conformation of the cells 

 change with age, but also that these changes operate in a great measure on the 

 exterior surface, — that is to say, on that side of their parietes, which, in the 

 hypothesis of their formation by layers, must exist from the first, and once con- 

 solidated, ought to change no more, unless from exterior and accidental frictions. 



