32 RAINEYj ON CARBONATE 0¥ LIME GLOBULES. 



consequence of their having arrived at maturity, and blending 

 with the calcareous element, the colouring of the margin of 

 the mantle being similar to that of the shell. Probably, this 

 process is slightly modified in some instances by an especial 

 gland providing the pigment incidentally to other functions it 

 may have to perform. Instances of this might, perhaps, be 

 found in those animals in which the shelly having arrived at 

 maturity, the lip is uniformly coloured. 



'' From these facts I am led to believe, and, I trust, not 

 without sufficient reason, that the shells of these animals are 

 formed by the coalescence of minute particles of lime on the 

 inner surface of a previously formed animal layer (epidermis) , 

 being attracted to it before they have time to form globules 

 by their attraction to each other, it being the inner, instead 

 of the outer, surface of this membrane, in consequence of its 

 greater thickness preventing the fluid passing through it. 



" This idea is, I think, strengthened by the fact that globules 

 of lime, in considerable quantities and of aU sizes, are found 

 in the mucus, on the surface, and also imbedded in the free 

 edge of the mantle of Paludina vivipara, and probably in those 

 of other moUusca, if carefully examined. 



" Yours truly, 



" C. Stewart. 



"St. Bartholomew's Hospital; 

 "Nov. 20, 1860." 



Besides the crystals above noticed, there are others which 

 I hope to describe in a future number of this Journal, my 

 present occupations taking up so much time as to render it 

 impossible now to prolong this communication ; I hope also 

 to extend the subject to the structure and development of 

 striped muscular fibre. 



