THE MUSEUM. 



39 



merr and Duhamel obtained, in fact, 

 a purple color from this species, which 

 they applied to some stuffs, and found 

 that it resisted the strongest lye. The 

 f;enus Murex is supposed by some to 

 have contained the species indicated 

 by Aristotle. 



Up to the present time, the produc- 

 tion of the Tyrian purple remains a 

 mystery. It was long thought this 

 fine dye was furnished by the stomach 

 and liver, but M. Lacaze-Duthiers has 

 demonstrated that the organ which se- 

 cretes it is found on the lower surface 

 of the mantle, between the intestines 

 and the respiratory organs, where it 

 forms a sort of fascia, or small band. 

 The coloring matter, as it is extracted 

 from the animals, is yellowish; expos- 

 ed to the light, it becomes golden yel- 

 low, then green, taking finally a fine 

 violet tint. While these transforma- 

 tions are in progress a peculiarly pun- 

 gent odor is disengaged, which strong- 

 ly reminds one of that of assafoetida. 

 That portion of the mantle which has 

 not passed into the violet tint is solu- 

 ble in water; when it has taken that 

 tint it becomes insoluble. The ap- 

 pearance of the color seems provoked 

 rather by the influence of the sun's 

 rays than by the action of the air. 

 The matter attains its final color, in 

 short in proportion to the power of 

 the sun's rays. 



It is a question how far the color 

 evolved under the solor rays remains 

 indelible. It is known that the con- 

 trary is the case with the coloring 

 matter of the cochineal insect, which 

 changes very quickly when exposed to 

 the sun. It is probable that it was the 

 remarkable resistance which this pur- 

 ple opposed to the rays of the sun 

 which recommended it to the ancients. 



The patricians of Rome, and the rich 

 citi/rens of Greece and Asia minor, lov- 

 ed to watch the magical reflections of 

 the sun on the glorious color which or- 

 namented their mantles. 



But to return to our humble shells. 

 Purpura lapillus [Fig. 27] is a thick 

 shell, oval, acute, with conical spire, 

 generally of a faded or yellowish 

 white, zoned with brown, and more or 

 less spotted. 



Purpura patula [Fig. 28] is very 

 common in the Phillipines, and is one 

 of the handsomest species; its geograph- 

 ical distribution has been a subject of 

 much inquiry. 



Purpura consul [Fig. 29] is one of 

 the large shells of this genus, and of 

 a fine salmon color, with brown brands 

 and a corona of spines. In the Jan- 

 uary number we will review some of 

 Harpa, Marex, Triton and Stromba. 



The Pearl. 



Pearls are not only highly prized as 

 objects of personal ornament, but form 

 the subject of an intensely interesting 

 and highly profitable study. 



The formation or growth of the 

 pearl has given rise to innumerable 

 and conflicting statements from those 

 who have given the matter careful 

 study. The growth of the pearl is not 

 yet fullv explained. It is definitely 

 known that pearls are formed by the 

 deposition of nacreous matter in con- 

 centric layers around foreign substances 

 which have happened between the 

 mantle and shell of the mollusc and 

 which had become a source of irrita- 

 tation. It is commonly believed 

 that the disturbing object is a grain 

 of sand, although this popular no- 

 tion seems untenable. Many emi- 

 nent conchologists, including Dr. 



