Scientific Intelligence. — Zoology. Ii87 



thicker the layer of mother-of-pearl on the inner surface of the 

 shell, the more capable, he conceives, is the individual of convert- 

 ing these coagula into pearls. There is, he admits, another va- 

 riety, originating in the presence of foreign bodies, such as grains 

 of sand, &c. between the shell and the integuments, which lie- 

 come enveloped in a layer of pearly matter ; and a third species, 

 as is well known, may be generated by boring into the shell, or, 

 indeed, originates sometimes without any external injury, mere- 

 ly in a diseased secretion of the mantle. — Dublin Medical Re- 

 port^ No. iv. p. V6% 



f.iilO. On the Reproduction erf Nerves^ by Tiedemann, — It is a 

 ifeW known fact, that nerves, after having been cut through, 

 have the power of uniting and growing together again. The 

 phenomena observed in this process are the following : In the 

 first place, the ends of the divided nerve recede from each other, 

 so as to leave an interval of from about two to six lines, or more, 

 between them. This is more striking in great than in small nerves. 

 It does not depend on their elasticity, as some have imagined, 

 but on the organic contractibility of tonicity of the neurilema, 

 and of the surrounding and connecting cellular tissue. The 

 proof of this is, that the same phenomenon does not occur in the 

 dead body on dividing the nerve. In consequence of the irrita*. 

 tion produced by the division, inflammation soon sets in, and the 

 nerves assume a red colour, and become thickened, generally for 

 the space of from half an inch to an inch, from the point of sec- 

 tion. These appearances are the more remarkable in the en4 

 connected with the nervous system, than in the other. Coagu-j 

 lable lymph becomes deposited around them, and minute vessels 

 appear in it. In consequence of the inflammation and the ei^ 

 fusion of lymph into the cellular tissue around the general sheath 

 and between the partial sheaths, a swelling or knot is produced 

 of the ends of the nerves, that on the upper end being the largest ; 

 similar bulbous swellings are found on the ends of nerves divided 

 by the amputation of a limb. After a few days the separated 

 ends become connected by the effused plastic lymph, which gra- 

 dually assumes a firmer texture, and shews less blood in itsves. 

 sels..^^The bulbs gradually approach each other, and at last 

 unite ; and thus the connection between the parts of the divided 



