EPITHELIOID MEMBRANES IN MONAXONID SPONGES 549 
Later development. The epidermis 24 hours after cutting is 
like that of the normal sponge. The coarse granules found in 
earlier stages are absent or present only in scanty number here and 
there. Pore canals that are open or closed in by pore membranes 
are abundantly present. The ectosomal skeleton is scanty. 
Pieces of sponge were kept in live boxes for a week and in these 
examination indicated that the ectosomal skeleton was practically 
like that of the normal sponge. The color of the new surface at 
this time was still like that of the interior, orange, while the old 
surface was orange with a distinct tinge of green. 
Summary. A comparison of the stages just described shows 
that immediately after the cutting coarsely granular mesenchyme 
cells approach the exposed surface in considerable number. 
Many of the migrating cells are doubtless originally free amoebo- 
cytes. The granular cells when they have reached the neighbor- 
hood of the surface appear as branched bodies freely intercon- 
nected. This layer of interconnected granular cells develops 
into the new dermal membrane. The cells at the surface become 
flattened and more closely set than the deeper elements from which 
they are no doubt recruited during the first few hours. 
They fuse to form the epidermis. Union between the cells takes 
place not through crowding so as to give rise to plane surfaces, 
but through the continued development of intercellular connec- 
tives. As these become more numerous and branched they give 
rise to a complex reticulum of protoplasmic strands. This inter- 
cellular reticulum becomes transformed into what we would 
usually speak of as a continuous sheet of protoplasm, although 
careful examination shows that even in the adult it has a finely 
reticular, possibly alveolar, structure. During the metamorpho- 
sis of the superficial granular cells into the epidermis, the cells 
loose their characteristic granules. The pore canals arise as 
excavations in the mesenchyme of the developing dermal mem- 
brane, and are covered in by the new epidermis which in such 
places constitutes pore membranes. 
THK JOIKNAI. OK EXPKRIMBNTAI, ZOOLOGY, VOL. 9, NO. 3. 
