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THE AMERICAN NATURALIST [Vol. LIII 



were at that time demonstrated within the "eyes," some 

 writers followed Joyeux-Latfnie (1882) in the opinion 

 that the ' ' dorsal eyes ' ' of Semper were in reality mantle 

 glands, corresponding to those undoubted glands found 

 in the related genus Oncidiella (cf. v. Wissel, 1898). The 

 more complete analysis of the histology of the mantle in 

 Onchidium by Stantschinsky (1908), nevertheless, proved 

 that the "dorsal eyes" do possess nervous structures ap- 

 propriate for photoreception, the retinulae being, in addi- 

 tion, of the inverted ("vertebrate") type. 0. fioridanum 

 possesses, however, repugnatorial mantle glands as well, 

 which are not associated with the dorsal papilla, these 

 last being relatively minute. 



The glands are comparatively large, but are easily 

 overlooked in an undisturbed Onchidium. The periphery 

 of the mantle has a frilled appearance, numerous tiny 

 projecting papillae giving it a serrated outline. If the 

 animal be disturbed, the tissues surrounding each of the 

 glands become erected, and 14 stout conical papillae, 7 on 

 either side and each with a terminal pore, become evident. 



If the animal is suddenly removed from the rock by 

 grasping its dorsum, the glands all become turgid, point 

 upward and inward, and quickly discharge by the con- 

 traction of their muscular investments. The secretion is 

 a viscid fluid, milk-white, non-miscible with sea-water, 

 and decidedly acid in reaction. Discharge is more easily 

 elicited in air than whc\n the animal is submerged. Under 

 water the secretion is expelled in long threads, but in air 

 the stream as il leaver llic ulaud breaks up into a fine 

 spray, which max Ix- -hot \n ;t di-tniiec of 12- ]5 cm. With 

 vigorous stiimdatioii. a- when \\u- hack of the Ourhidium 



gland as a stream almut O.i' inin. In .li!ii„rt. r, xxhi.'h is 

 often too stout to form fine (Ir.ipids. h, natiii-p. \unv- 

 ever, the initial rcpngiiatorial <h-^<-hai-,. h^.. copious; 

 it then takes the t'onii of a liiir sprav, ahnost invisible, 

 which may be thrown for as much a< lo cm., or about ten 

 times the length of the Oi/i-linlnim. 



