MATERIALS FOR A MONOGRAPH OF THE ASCONS. 823 
the larva, while in the Clathrinide the nucleus migrates 
into a position near the base of the cell. 
Bidder (1898, p. 73) has pointed out that in Leucoso- 
leniide the pore-cells, or, as he terms them, pylocytes, are 
not on the surface as in the Clathrinide, but at the 
bottom of short canals lined by the dermal epithelium. I 
am able to confirm this statement. Fig. 72 shows four poro- 
cytes and their relation to the dermal epithelium, drawn 
from the gastral aspect, the spicules and other cells being 
omitted. The structure of each pore and its enclosing cell is 
exactly as in Clathrina. 
The amcebocytes in Leucoselenia are not so distinct 
from the other tissue-cells in appearance as they are in 
Clathrina, but can be distinguished by their larger nucleus 
(Figs. 49, 71, amc.). I found in Leucosolenia the same 
minute wandering cells, very abundant in some places, that 
I described formerly in Clathrina (fig. 71, ame.?). 
In the great majority of works upon sponge-histology, it 
is customary to distinguish and to describe a class of con- 
nective-tissue. cells, stellate or bipolar in form. Without 
wishing to make statements about other sponges, it is my 
firm opinion that no such cells occur in Ascons. In surface 
views of the body-wall it is easy to make out the various 
classes of cell-constituents, namely, dermal epithelial cells, 
porocytes, amcebocytes, scleroblasts attached to the spicules, 
and collar-cells, with the addition, in certain specimens, of 
generative cells. No separate connective-tissue cells are to 
be seen. In sections of the body-wall, however, the spicules 
are always more or less displaced (compare fig. 55), and 
_ their scleroblasts, left in position, give the impression of 
separate connective-tissue cells. If, however, the stellate 
cells, frequently described as being numerous, really occur, 
they should be visible in surface views, in which their 
absence is, in my opinion, a convincing proof that no such 
class of tissue-elements occur in these sponges. 
I come now to a remarkable class of cells, which I dis- 
covered first when studying the gastral rays of the quadri- 
