226 (Scientific Proceedings, Royal Dublin Society. 



Fenestra! Crlands. — The above-mentioned " cancellated 

 spaces," or fenestrse are the expression of somewhat complex glan- 

 dular infoldings of the epidermis in those regions, for which I pro- 

 pose the provisional name of " Fenestral glands." 



Each " cancellated space " extends, transversely, from that spot 

 where the upper surface of the foot joins the body proper outwardly 

 as far as the longitudinal fold on the underside of the mantle ^ ; 

 and longitudinally it extends from just in front of the anus to about 

 the region of the renal duct, and therefore some little distance 

 behind the generative orifice. The extent of the area and the 

 complexity of the gland appear to vary considerably in different 

 specimens of the same species.^ 



The epidermis of the ventral surface of the foot is composed of 

 columnar cells ; these become somewhat shorter on its upper surface, 

 and in the region in question again become markedly columnar, 

 and very large in size. They resume their ordinary character in 

 passing over the longitudinal fold ; and external to it they secrete 

 the calcareous spicules characteristic of the species. 



The gland simply consists of the epidermis, composed of large 

 columnar cells of the definite areas above mentioned, which is 

 thrown into a number of folds, or produced into slightly contorted 

 and branched tubes, thus giving a remarkable labyrinthine appear- 

 ance to transverse sections of that region of the body. Between 

 the variously cut sections of these tubes are small patches of poly- 

 gons which are, of course, merely the transverse or oblique sections 

 of the cells or other cseca of the gland. See figures 2-4, 

 Plates X. and XI. 



It would be premature at present to discuss the nature of these 

 curious infoldings : in the allied Ch. cinereus they appear to be in- 

 conspicuous, and to be absent or rudimentary in other forms. 



Dr. Hubrecht (9) has described a pair of simple csecal glands in 

 Proneomenia sluileri (Hbrcht.) which open into the anal cavity, and 

 which secrete extremely delicate threads ; anteriorly they are en- 

 closed in a strong muscular investment. Hubrecht suggests they 



1 This fold is the " fringe " or " true mantle edge " of Dall (7), and the " longitu- 

 dinal fold" or "lateral hand" of Haller (11), 



~ For example, in all my specimens of Ch. ruber from Norway the gland is much 

 infolded; hut in a specimen from "Eastport, N. E. America" (for which I am in- 

 debted to the courtesy of the Eev. A. M. Norman), the gland is a great deal simpler. 



