BIOLOGY. 
Spong. 7 
secondary rays. Stauractin , cross-shaped Tetractin, the rays of which 
lie in one plane (chiefly for such spicules with cylindrical, terminally 
rounded, and often spined rays). 
Topsent (51) has found in an Esperellid remarkable nail-like spicules, 
for which he proposes the new name Exotyl. 
Weltner (55) describes the skeleton of Ephydatia fluviatilis. The 
fibres arise from a basal Spongin-plate, in which “ nuclei,” remnants of 
the Spongoblasts which had originally secreted this basal plate, are met 
with. In the radial main fibres as many as 12 (or even more) spicules lie 
side by side, in the transverse connecting fibres only 2-6. The quantity 
of Spongin-cement, which holds the spicules together, is very small, 
smaller than ill other Spongillids. The spicules of the whole skeleton 
weigh one-thirteenth of what the Sponge to which it belongs weighs in 
the fresh state. 
d. Epithelia and Cuticula ( 18 , 55 ). 
Weltner (55) states that the outer surface and all internal cavities of 
Ephydatia fluviatilis , with the exception of the ciliated chambers, are 
clothed with an epithelium composed of flattened polygonal cells. Round 
the dermal pores sickle-shaped cells are situated. The thin trabecuke 
traversing the subdermal cavities appear to be composed of a single row 
of modified epithelial cells. A kind of cuticule is met with in the lower 
part of the interstitial layer of the dermal membrane. The collar-cells 
in the chamber walls are either close together, and then mutually com- 
pressed into prisms with polygonal transverse section ; or they stand 
further apart, and then have a circular transverse section. In the latter 
case hyaline ground substance, similar to that of the interstitial layer, 
occupies the intervals between the collar cells. The collar is, in the 
living collar cell, twice as long as the body, and the flagellum has a per- 
pendicular root which extends down to the nucleus. 
e. Cortex ( 51 , 55 , 56 ). 
According to Weltner (55) the dermal membrane of Ephydatia 
fluviatilis is clothed on both sides with flat epithelium, and contains, in 
the interior, a cuticular structure. 
In Gompliostegia loricata , according to Tofsent (51), the nail-like 
“ exotyles” form, standing side by side vertically close together in the 
skin, a strong armour. 
A somewhat similar armour, composed of stout-shafted triaens, has been 
found by Winchell & Schuciiert (56) in Anomalospongia reticulata. 
f. Interstitial Layer ( 18 , 35 , 55 ). 
Minchin (35) is of the opinion that the interstitial layer of Sponges 
is derived mostly from the ectoderm, partly also from the entoderm, and 
not truly mesodermal. 
Similarly Hasckel (18) considers the interstitial layer as a mesenchym 
populated by ectodermal cells, and remaining throughout closely con- 
nected with the ectoderm. 
According to Weltner (55) three kinds of cells occur in the inter- 
stitial layer°of the dermal membrane in Ephydatia fluviatilis. Many of 
these are connected by processes which appear to be movable, like Pseudo- 
podia, and continually sever old connections and form new ones. In the 
interior of the Sponge, the same three kinds of cells occur, and eight other 
