ORGANS OF SECRETION. 109 



date. The Roman law prohibiting the use of purple garments to 

 any but the imperial family, was a deathblow to this industry, 

 which thenceforth rapidly declined. During the middle ages the 

 very existence of such a dye was considered fabulous ; but with 

 the revival of the arts and civilization its properties were redis- 

 covered, and for awhile successfully utilized. Chemistr}^ has 

 now supplied us with even more brilliant colors, whilst saving- 

 much of the cost of procuring material. 



An anal gland accompanies the purple gland in Murex and 

 Purpura and has not been discovered in other mollusks. It lies 

 on the left side of the rectum and consists of a central canal 

 with lateral branches having a dendritic appearance. It opens 

 on the edge of the anus, and by pressure its brownish contents 

 may be made to issue. The function of this, as well as of the 

 purple gland is unknown. 



The Mucus-Gland lies in the middle portion of the cover of 

 the respirator}^ cavity in most prosobranchiates ; its tough secre- 

 tion is discharged through the respiratory opening in extra- 

 ordinar}^ quantity, especially when the animal is handled. 



The glands of the mantle-border of Oncidiella are remarkable 

 for their size and the regularity of their position. They all open at 

 the summit of little cutaneous eminences, and they secrete an 

 abundant whitish liquid. 



Mucous glands are largely developed in the pidmonata geophila 

 or terrestrial pulmonates. There exist in Limax, Helix, etc., a 

 series of unicellular glandules the contents of which are poured 

 into a large canal which opens on the anterior part of the body 

 between the head and foot. This organ was discovered by 

 Kleeburg, after whom it is named. Its functions have been 

 variously interpreted, and Leidy has thought Kleeburg^ s Sinus 

 an olfactory cavity. 



In Arion, Helicarion, Pai-marion, N'anina, etc., there is a 

 mucous gland opening by an orifice (mucous pore) at the dorsal 

 posterior extremity of the foot : its product is very abundant. 



Many gastropods and bivalves secrete a glutinous thread, 

 strong enough to support the weight of their body. Thus the 

 young of certain limaces descend from one branch to another, 

 suspended by a filament adhering to their tail. Ghond^'ojDoma 

 denfatum produces a filament which passes between the oper- 

 culum and the wall of the shell, by which the animal suspends 

 itself to branches or leaves. Numerous filaments fix in like 

 manner the Cerithidea to brackish-water plants. The fresh-water 

 univalves Physa, Limnaea, Planorbis, Neritina and Bithynia, 

 and the bivalve genus Sphaerium, suspend themselves in the 

 water in like manner; Rissoa, Odostomia, Eulima, Cerithium are 

 examples of marine mollusks possessing a like faculty. Litiopa, 

 a small gastropod, lives abundantly in the floating fuci and 



