EPITHELIOID MEMBRANES IN MONAXONID SPONGES 543 
of the pore, and this nucleus is (perhaps only passively) associ- 
ated with the formation of the pore membrane. 
Some details in the structure of the epidermal layer remain 
to be mentioned. The irregular distribution of the nuclei has 
been noted. They are small and uniformly exhibit only a nuclear 
membrane and a few chromatin granules in the nucleoplasm. No 
cases of division were observed, although mitotic figures in amoe- 
bocytes of the mesenchyme were noticed not infrequently. Round 
each nucleus or group of two or three is a more deeply- staining 
area which appears finely granular or granular and reticular. The 
rest of the membrane stretching between the nuclei and over the 
pore canals exhibits a fine reticular structure. The reticular 
structure is found everywhere, but is most distinct in the thin 
pore membranes. Discrete granules are absent or nearly absent 
in the epidermal sheet. It should be understood that the reticu- 
lar appearance of the epidermal layer is perhaps only the optical 
expression of an alveolar structure. To demonstrate the reticu- 
lar appearance a good immersion objective is necessary. I have 
chiefly used Zeiss 2 mm. ap. 1.30 but also Zeiss 2 mm. ap. 1.40, 
with comp. oculars 6 and 8. Very white clouds on sunny days 
afford satisfactory- light. 
Results with other fixatives 
Material fixed by other methods confirms the account just 
given. 
Picro-sulphuric. Tangential sections and strips of epidermis 
were prepared from material fixed in picro-sulphuric. The stain- 
ing was as for the alcoholic material, and the preparations gave 
the same results. Absolutely no cell boundaries exist. The 
internuclear sheet more commonly appears finely granular rather 
than reticular. Possibly this is due to a deeper staining of the 
nodal points. But the fine reticular structure comes out well in 
places, especially in the pore membranes. Discrete granules 
such as are found in mesenchyme cells are either entirely absent 
or are found only in very small number here and there. 
