ORGANS OF SECRETION. 48 



a prolongation of the kidnej^ Imt is oftcm separated from the 

 latter bj a diaphragm ])erfor:ited by a number of holes which are 

 encircled b}' muscular fibres. Within, a number of longitudinal 

 folds are to be observed, and it is covered throughout with 

 ciliated (^])ithelium. Tlie ureter is usually filled with water and 

 it is possible that it may have some other signilicance than a 

 mere efiercnt duct. 



The mucus gland lies in the middle portion of the cover of the 

 respiratory cavity in most prosobranchiates ; its tough secretion 

 is discharged through the respii-atory opening in extraordinary 

 quantity, especially when the animal is handled. 



The puri)le gland accompanies or is a modification of the 

 mucus gland. It is only found in a portion of the prosobran- 

 chiates ; among them, lioth the typical Muricidaj and the Pur- 

 puridae. The peculiarity of the fluid secreted by this gland is, 

 that originally colorless or yellowish, a short exposure to sun- 

 light changes it to a brilliant violet oi> reddish color, at the same 

 time giving oft' a very penetrating fetid odor. The cause of this 

 photographic change of color is unknown, but the knowledge of 

 it caine to mankind in very early ages, and Tyrian purple was 

 the most highly prized and most beautiful dye known to the 

 ancients.* 



Pliny states that in his time the purple dye was obtnined from 

 the Buccinum and the Purpura. The moUusk now known as 

 Murex trunculus is generally supposed to have been that j)rinei- 

 pally used by the ancients in obtaining the Tyrian purple. It is 

 related that the discovery of the dye is due to the dog of a Tyrian 

 nymph, which crushing some of these shells in its teeth, its mouth 

 became stained with purple. It is possible that the fragile lanth- 

 ina may have been thus crushed, but the shells of the Muricidte 

 Avould resist the dog's teeth. To be exact, this event occurred 

 1500 B. C The color was so beautiful that the fair nymph ex- 

 pressed to her lover, Hercules, her desire to have a robe of simi- 

 lar hue. Hercules, of course, gratified her. It is evident that 



* SeeLucaze-Duthiers' (Ann. Sc. Nat., xii, 5, 1859) exhaustive "Meraoire 

 sur hi Pourpre," an exceedingly interesting paper, ilkistrated by speci- 

 mens of the color resulting from various applications of the dyes obtained 

 from Murices, Purpuras, etc. See also Smithsonian Report, 1863 ; LovelVa 

 Edible MoUusks, p. 134 ; Orimaud de Caux, Rev. et Mag. Zool., 34, 1856. 



