EEPOET ON THE TETEACTINELLIDA. 
223 
style, a slow contraction invariably follows, and this would lead us to expect the 
presence of such cells, and in such positions, as those here described. The chones open 
into subcortical crypts, which extend horizontally beneath the cortex, and are continued 
inwards as the incurrent canals. 
The mesoderm of the choanosome is a very distinct sarcenchyma, except where it forms 
the walls of the larger canals. It then becomes either collenchymatous or fibrous. The 
flagellated chambers (PL XXL fig. 12) measure from 0‘0276 to 0'03 mm. in breadth by 
0’02 to 0'0276 mm. in length, the prosopyle is usually about O’OOS mm. in diameter, the 
apopyle O’OOS to 0’015 mm., the prosodus is usually very short, but in some instances is 
prolonged to a length of 0’02 mm. 
The spicules of the spicular fibres traverse the cortex and extend for all distances up 
to 1’6 mm. beyond the surface (PI. XXL fig. 14); the hispidation thus produced may be 
regarded as a stage in the process of expulsion of the spicules. 
It may be worth while finally to mention the occurrence of an abnormal form of 
dichotrigene, in which the deuterocladi have themselves become bifurcate, producing trito- 
cladi. This appears to stand in correlation with the fact that the deuterocladi are not 
always extended tangentially, but point forwards as well as outwards, hence they are 
liable to bend at some distance from their origin into the tangential position not at first 
assumed ; bending frequently results in branching, and such appears to have been the 
case in the trichotrisene here recorded. 
Cy ionium glariosus, Sollas (PI. XX. figs. 14-21; PI. XL. figs. 3, 4), 
Cydonium glariosus, Sollas, Prelim. Account, Sci. Proc. Eoy. Dubl. Soc., vol. v. p. 196, 1886. 
Sponge (PL XX. fig. 14). — More or less spherical, attached. Oscules not distinguish- 
able from the pores, which have the usual sieve-like arrangement. The collenchymatous 
layer, which lies beneath the external epithelium and its associated chiasters, is crowded 
with coarse grains of sand, and traversed by radiating pencils of short oxeas ; and by the 
distal ends of the radiating somal megascleres, particularly of the protrisenes, the cladomes 
of which frequently lie within it, but sometimes project beyond the outer surface to the 
exterior (PL XL. fig. 3). 
Spicules. — I, Megascleres. 1. Somal oxea, fusiform, usually curved, somewhat 
abruptly pointed, more so at the distal than proximal end ; 1 ’8 5 6 by 0’026 mm. i 
2. Cortical oxea, fusiform, abruptly pointed, 0’3o to 0’4 mm. by 0’0158 mm. 
3. Orthotrisene (PL XX. fig. 15), rhabdome conical, attenuated to an excessively 
sha«rp point ; cladi simple, diverging outwards, at first with a slight forwardly, and after- 
wards with a slightly back\Yards directed curve. Ehabdome 2 ’8 5 6 by 0’0516 mm., chord 
0’464 mm. 
4. Protrisene (PL XX. fig, 16), rhabdome longer and slenderer than in the preceding. 
