310 DR- H. LYSTER JAMESON ON 



salts secreted and of the periodicity of the secretion as determined 

 by the control, or loss of control, of the secreting epidermis. 



In fact, if my interpretation is correct, the processes involved 

 in the bviilding of the shell are the visual chemico-physical ones 

 which govern cr3'stallisation in colloidal media* controlled and 

 limited by the time-factor which is a function of tlie activity 

 of the living cells. 



It is less easy to imagine the conditions which determine 

 the transformation of the fluid albuminous secretion into the 

 leathery conchyolin. One is naturally tempted to postulate 

 a chemical ti^-jnsformation as a direct or indirect result of the 

 action of nascent CaOOg, as in the case of the calcoglobin in 

 Harting's bodies (12) ; but the formation of this substance 

 apart from the lime-salts, e. g. in the inner layers of the perio- 

 stracum and in amorphous repair- substance, and in the cfise 

 of shells grown in lime-free media (Moynier de Yillepoix, 28, 

 p. 122), seems to negative this; and it may well be that this 

 change to sa\ insoluble albuminoid is directly brought about 

 by the action of the secreting cells themselves, or follows from 

 the chemicjxl composition of the secretion as shed. 



(12) Abnormal and Pathological Phases of the 

 Shell-Substance. 



For a study of the beginnings of Ceylon pearls, a consideration 

 of the variations in the shell-substance, when it is secreted 

 under abnormal conditions, either on the surface of the shell 

 or of a growing pearl, is of importance. 



Where the normal rhythm of the process of shell-secretion is 

 interrupted, e. g. by injury to the shell, or the intrusion between 

 the epithelium and the nacre of a foreign particle or by other 

 disturbances less easy to explain, certain irregularities in the 

 process of secretion occur, resulting in an altered product. 



In the simplest case such a disturbance results in a modification 

 pi'oducing a granular appearance of the conchyol in-lay ers of 

 the nacre. This modified substance I propose to call " granular 

 repair-nacre." In sections made through this substance, after 

 decalcification, the normal stratification is obscured by a highly 

 granular appearance which seems to be due to an infinite 

 nvimber of connections between the successive conchyolin-layers 

 resulting in a distinctly alveolar membrane. This is shown 

 in text-fig. 38 (rejy.nac), which is taken from an artificial 

 " blister " produced by the writer in Margaritifera margariUfera 

 after the " Linnseus" method, in British New Guinea in 1899. 

 The foreign body was inserted near the mantle- margin, and the 

 mantle secreted first a double layer of the prismatic subtance, 



* Biedcrmann (2), p. 171, recogtiises tliat tLe structure of the shell is essentially 

 reducible to crystallisation processes, the influence of the cells being limited to the 

 composition of the fluid, and perhaps the orientation of the primary centres of 

 crystallisation, But I \vould add to these influences the periodicity of their 

 action. 



