and extra-vasadar Snlstances in living crganhed Bodies. 5 



complete fonnation, and only ad'aere mechanically to the living 

 parts for a time. 



The most apposite illustrations and the most positive instances 

 cf nnion between vital and extra-vital parts are to be fomid in 

 the testaceous tribe of animals. After a long continued and 

 carefui investigation, I am fully convinced tliat the shells of all 

 the Fermes oi' Llniisens are extra-vascdar from their commence- 

 ment, and remain so during the whole of their connexion with 

 ■the living creature. The first production and the growtli of 

 those shells always de])end u})on a deposit of material thrown 

 out from the surface of the body of the living animal. The 

 figure and colour of the several parts of those shells in every 

 species depend upon the sliape and the colouring glands of the 

 modelling organs. Fractures are repaired by spreading a cre- 

 taceous fluid over the inner edges, and never by anv exTidation 

 from the fractured parts, since they retain always the squared 

 broken surfaces after such repairs. Extraneous bodies are 

 equally covered with shell, whether they are in contact with the 

 parent shell or not. The first may be seen in the frequent en- 

 velopment of Nereides in the comnion ovster ; the latter has been 

 often ascertained by experiments made for the purpose of crea- 

 ting artificial pearls, and which might, if skilfully practised, vet 

 prove very successftd. The borings of parasitical vermes into 

 shells are never filled up, or the bored surfaces altered, unless 

 such bornigs penetrate into the cavity where the living animal 

 dwells, and then the a])ertures are universally plugged up or 

 smeared over with pearly matter. T!ie water-\vorn external 

 surfaces of old shells and other external abrasions are never re- 

 paired, which is to be seen in old living oysters exposed to the 

 moving friction of currents or strong tides, i'n the worn-off spines 

 of the Pholas Dadylus and in the convex points of the two 

 valves of old Myiili ; especially the Mytilus mtatimis. ] have 

 sought in the most extensive collections of the metropohs for 

 examples of fractures, and other injuries wliich have occurred to 

 the shells of living vermes, and I have collected many remark- 

 able specmiens : they all demonstrate the same results without any 

 exception. I have made numerous experiments upon the gar- 

 den snad Hehx vcmoralis, by fracturing and breaking away the 

 shell in various parts, and have always found the repairs to be 

 effected from witlun and by smearing over an epidermoid varnish 

 and then by plastering the inner surface of that film with suc- 

 cessive calcareous laminae. I have in vain attempted to inject 

 the shells of recent vermes from the vascular parts of their bodice 

 and am fully satisfied that none of their albuminous or gelatinous 

 testaceous membranes were ever at any time traversed by vessels • 

 nideed Ihcy do not possess any of the reticular texture or ar- 

 "■ ^ borescent 



