568 
H. V. WILSON 
recenth^ metamorphosed Axinella, Alaas ('93, p. 350, pi. 21, fig. 
37) finds that the surface views of all his preparations speak for 
this interpretation. If this idea be true, the porocyte occupies the 
thickness of the dermal membrane, extending from the outer 
surface to the subdermal cavit\\ Delage in describing the recently 
metamorphosed Spongilla ('92, p. 398, pi. 16), discusses whether 
the pores be intercellular gaps or intracellular structures, and thinks 
they are probabh^ the latter. The relation of the porocyte, pro- 
vided it exist, to the dermal membrane as a whole would here be 
problematical, since according to Delage, when the pores appear 
the mesenchyme and the inner epithelial layer of the dermal mem- 
brane have not developed. Weltner ('07, p. 276) too is led by his 
observations on Ephydatia to regard the dermal pores as intra- 
cellular. He speaks of them as perforations of the pinacocytes 
and mentions that the latter can change their shape. It is evi- 
dent that a more extended, comparative study of the point is 
needed. It is not impossible that beneath the appearances 
recorded by the above named authors will be found the structural 
conditions described here for Stylotella and Reniera. In passing 
it may be noted that both Delage and Maas figure the epidermis 
as without cell boundaries.^ If cell boundaries really exist, it is 
remarkable that they should not be visible in such thin mem- 
branes at a magnification of 750, the magnification at which 
Del age's figures are drawn. 
Canal epithelium. The loose epithelioid membrane which I 
have found lining the canals of Stylotella cannot be an isolated 
structure. Several facts recorded in the literature indicate that 
it may possibly be a common type. From among these I may 
mention the following: Sollas ('88, p. xxxvi) describes the epithe- 
lium lining the cortical canals of Pachymatisma as ''without defi- 
nite cell outlines, but the contained protoplasm, however, is very 
admirabh' displayed, as a superficially extended film produced 
into innumerable fine, sometimes branching threads." ''The 
thread-like processes of adjacent cells seldom appear to unite, 
'Delage, loc. cit., pi. 16, fig. 9 b, for Spongilla; pi. 21, fig. 5 a, for Aplysilla. 
Maas, loc. cit., pi. 21, fig. 37, for Axinella. 
