EPITHELIOID MEMBRANES IX MOXAXOXID SPOXGES 565 
examination of the '^Challenger" collections ('87) to occur on the 
dermal and canalar surfaces in many of these sponges. Schulze 
regarded the layer as an epithelium, stating, however, that he 
was not able to detect the contours of the cells. Ijima ('01, '04) 
finds that such membranes do not consist of differentiated epi- 
thelial cells distinct from the underlying trabecular tissue (essen- 
tially a plexus-like syncytium of mesenchyme elements), but are 
produced simply by the flattening out of the superficial trabeculae. 
In some cases there is really no bounding membrane, since the 
general syncytium preserves at the surface its character as a 
reticulum. Schulze is inclined ('04, p. 202) to assent to Ijima's 
position and remarks ^'Es ist also wohl anzunehmen dass hier" 
(in the hexactinellids) ''die Differenzierung der oberflachlich lie- 
genden Gewebszellen zu echten epithelialen Pinakocyten unter- 
blieben ist." The permanent condition of a hexactinelHd would 
thus seem not to be far removed from that of a monactinellid 
(Stylotella) which is in process of regenerating its epidermis. 
Rarely it may happen that monactinellids linger permanently 
at this low stage of histological development. Suberanthus as 
recorded by Lendenfeld ('96, p. 172) seems to be a case in point: 
"Bei Suberanthus flavus ist die ausserste Gewebelage aus einer 
dichten, vielschichtigen Lage von unregelmassigen, massigen, 
multipolaren Zellen zusammengesetz. Die aussersten von diesen 
sind auf der Aussenseite abgeflacht und bilden das aussere Epithel, 
unterscheiden sich aber sonst in keiner Hinsicht von den tiefer 
liegenden." 
In the following sponges the records leave it uncertain what is 
the structure of the epidermis. In Chondrosia and Chondrilla 
(Schulze '77, pp. 18, 20, 23, 27) an epithelium does not occur on 
the dermal surface, which is covered with a thin, finely fibrous 
or homogeneous cuticular layer that is possibly formed by the 
fusion and metamorphosis of cells. In Euspongia (Schulze '79 a, 
p. 626) it is uncertain whether the epidermis is composed of dis- 
tinct cells. In Hircinia (Schulze '79 b, p. 16) the structure of the 
epidermis is uncertain. Some observations would indicate the 
presence of distinct cells, others that no cell boundaries exist. 
In Halisarca Dujardini (Schulze '77 a, p. 38) the dermal surface is 
THE JOURNAL OF EXPEBIMENTAL ZOOLOGY, VOL. 9, NO. 3. 
