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ARTHUR DENDY. 
number of smaller areas (fig. 4, p. a.), and as the latter are 
much better defined and more constant in size and relations 
than the former, it is better to apply the term pore-areas to 
them. These smaller areas appear to be strictly comparable 
to the pore-sieves of Phakellia ventilabrum, var. con- 
nexiva, or the pore-areas of Myxilla nobilis (14). Each 
one is an irregularly rounded or oval area, about 0T9 mm. in 
diameter, overlying a subdermal cavity, and each contains 
some five or six oval or rounded pores (fig. 4, p.) averaging 
about 0 - 05 mm. in their longer diameter. 
The most satisfactory way of studying the arrangement and 
form of the pores in this and many other Sponges is to slice off 
as thin a portion as possible of the surface, and stain and 
mount in balsam in the usual way, without cutting sections. 
Fig. 4 represents such a preparation seen from above as a 
transparent object. The pores may also be seen in sections 
taken at right angles to the surface (fig. 2, p.), but in the 
present case it is rather difficult to obtain satisfactory sections 
of this kind owing to the presence of the sand grains in the 
ectosome. 
(b) The Subdermal Cavities. 
In this, as in my previous paper (9), I use the term sub- 
dermal cavities in the sense defined in the Report on the 
“Challenger” Monaxonida, i.e. to mean the spaces into which 
the pores directly lead. Sollas, in his article on Sponges in the 
‘ Encyclopedia Britannica 5 (17), appeal’s to make use of the 
term in a different sense, as synonymous with subcortical 
crypts, while he applies the term chones to the structures 
which I term subdermal cavities. The homologies of 
these various structures are not at present sufficiently under- 
stood to enable us to give them a really satisfactory nomen- 
clature, and so I prefer to use a purely empirical one. The 
term subcortical crypt is used by Sollas and myself in the 
same sense, i. e. to mean the space underlying the cortex or 
ectosome into which the subdermal cavities (chones of Sollas) 
lead. 
