EPITHELIOID MEMBRANES IN MONAXONID SPONGES 563 
that loose epithelioid membranes such as I have found in Stylo- 
tella perhaps occur with some frequency in place of typical epithe- 
lia composed of polj^gonal cells fitting together neatly by straight 
edges. The covering layers of surfaces exposed to the water are 
certainty less uniform in sponges than was supposed some years 
ago to be the case. The hexactinellids in particular depart from 
the common condition. In these sponges, as Ijima's important 
discoveries seem to show, the covering layers in question can not 
be regarded as epithelia at all. 
In the following sponges the occurrence of epithelia on the 
surface of the body, or lining the canals, or in both situations, 
is well established. 
Calcarea. In Sycandra (Schulze '75) the dermal and gastral 
surfaces are covered with an epithelium composed of a single 
layer of flat polygonal cells which fit together neath'. In Grantia 
according to Dendy ('91a) the epidermis is a simple flat epithelium 
and the inhalent canal system is lined with a similar layer. In 
Vosmaeropsistoo, Dendy ('93) finds that the epidermis and canalar 
lining are simple flat epitheha. In Clathrina, Minchin ('00) finds 
the dermal surface covered with flat polygonal epithelium cells, 
between which are intercalated the peculiar pore cells. In Leuco- 
solenia, Dendy ('91 b) finds the dermal surface covered with thin 
fiat polygonal epithelium cells. The more recent investigations of 
Urban ('06) show that while the flat cell is the common type, the 
epidermis also includes cells of other shapes, some cylindrical, 
some flask-shaped, the latter probably glandular. Minchin ('08) 
confirms Urban's account as to the variation in shape of the epi- 
dermal cells in this genus. 
Carnosa. In Chondrosia and Chondrilla (Schulze '77 b) the 
canals are lined with a simple flat epithelium. In Plakina (Schulze 
'80) the dermal surface and canals are covered with a single layer 
of flat epithelium cells that are flagellated. In Plakortis (Schulze, 
loc. cit.) the conditions are similar except that the cells are prob- 
ably not flagellated. In Corticium, Schulze ('81) finds that the 
dermal surface is covered with flat epithelium cells. The canals 
of this genus are lined in places, according to Lendenfeld ('94, 
p. 74) with columnar epithelium. 
