214 MisceUa neous. 



MISCELLANEOUS. 



ox THE NATURE OF POLYPIDOMS. 



M. H. Milne Edwards, in a valuable paper on the nature and 

 growth of Polypidoms, published in the December number of the 

 ' Ann. Scienc. Nat.', after relating numerous observations on the 

 structure of the polypidoms in various tribes, concludes his able ar- 

 ticle in the following words : — " The various facts which we have ex- 

 amined seem to prove that the current opinion relative to the nature 

 and to the mode of formation of the polypidoms is inaccurate, and 

 that these bodies, far from always being external incrustations and 

 without any organic connexion with the animals which produce 

 them, are integral parts of these beings, and consist of an organized 

 tissue, the substance of which becomes charged more or less with 

 corneous or calcareous matter deposited at its base, and the nutrition 

 of which is effected by intus-susception. In all these animals there 

 is a tendency in the tegumentary and reproductive portion of the 

 body to harden, but the degree this solidification reaches varies much, 

 and this alone determines the differences which exist betweeen the 

 species distinguished by zoologists under the names of }iaked Polypes, 

 Polypes with flexible polypidom, fleshy Polypes, and Polypes with 

 stony polypidom. The cartilaginous or stony polypidom of a Sertu- 

 laria or of a Zoanthus, is not, as is usually stated, a habitation which 

 these animals build ; it is in some measure their membrane which 

 forms the solid structure of their body, and which, in the same man- 

 ner as the skeleton of vertebrate animals, assumes at one time a 

 membranous form, at another a cartilaginous texture, and some- 

 times a condition in some degree osseous." 



[A contrary opinion is taken by Dr. Johnston in his article on 

 British Zoophytes, in the • Mag. Zool. and Bot.' vol. i. p. 440. 

 *' Now when we trace the formation of this axis through the various 

 genera, from its first appearance in the form of scattered crystalline 

 spicula until it graduates into a solid continuous rod, we can scarcely 

 doubt its inorganic and extravascular character ; it is the crystalli- 

 zation of calcareous matter excreted by the living polypiferous bark, 

 and once excreted, beyond their power to change it, excepting by 

 the addition of material of the same quality." — Edit.] 



COMPARISON OF THE STRUCTURE OF SUCCULENT PLANTS WITH THE 



SIGILLARI^, 



M. Link exhibited at the meeting of the Berlin Academy on the 

 23rd of July, 1838, some drawings showing the structure of the 

 stem of arborescent succulent plants, \\i\h reference to the alleged 



