564 
H. V. WILSON 
Tetractinellida. In Craniella and some others of the ''Chal- 
lenger" tetractinellids Sollas was able to distinguish epithelial cells. 
He does not state whether the cells in these cases were epidermal or 
canalar ('88, p. 36). In Geodia and Ancorina Lendenfeld finds 
('94, p. 74) that the canals are lined in places with massive cells. 
Monaxonida. Among the Clavulina Lendenfeld finds ('96) 
in Tethya, Suberites, and Polymastia that the epidermis consists 
of flat epithelium cells. In Vioa, Suberanthus, Astromimus, and 
Papillella he finds the canals lined with epithelium cells which in 
some cases are flat, in others high, the two varieties perhaps only 
representing different physiological states of the same elements. 
In Suberites, Thomson ('86) observed that the epidermis consisted 
of a single layer of small, polygonal, and apparently unequal cells. 
Among the halichondrine monaxonida the Spongillidae are 
perhaps best known. In these sponges (Ephydatia) Weltner 
('96, '07) finds the epidermis and canal lining made up of flat 
epithelium cells (pinacocytes). Delage and Herouard describe 
('99, p. 176) the same condition as obtaining in Spongilla. Accord- 
ing to W eltner the epidermal cells include the pores which would 
therefore be intracellular. 
Keratosa. In Aplysina (Schulze '78 a) the dermal surface 
and canals are covered with flat epithelium cells. In Spongelia 
(Schulze '78 b) the same condition occurs. In Euspongia and 
Hircinia (Schulze '79 a, b) the canals are lined with flat epithelium. 
In Aplysilla (Schulze '78 a, Lendenfeld '89) the epidermis and 
canalar lining are made up of flat cells. In Dendrilla and Halme 
Lendenfeld ('89) finds that epidermis and canalar lining are made 
up of flat epithelium cells that are flagellate. In lanthella (Len- 
denfeld '89) the epidermis consists of flat cells. 
Myxospongida. In Oscarella lobularis (Schulze '77 a) the der- 
mal surface is covered with a single layer of fairly thick cells that 
are flagellate, and the canals are lined with a similar layer. In 
Halisarca Dujardini (Schulze '77 a) the canals are lined with 
flat simple epithelium. 
In the Hexactinellida true epithelia appear not to be present 
either on the surface or lining the canals. A thin nucleated pro- 
toplasmic \siyer to be sure, has been known since F. E. Schulze's 
