HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 309 
Canal-system. The pores of the dermal sieves on the outer side of the body 
lead into wide canals extending into the interior. Other still wider canals extend 
up to the gastral sieves on the inner face of the cup. Between these wide canals, 
the former of which are, no doubt, afferents and the latter efferents, a tissue is 
found containing narrow canals, and rather densely packed small flagellate 
chambers (Plate 84, fig. 2). The sections of these flagellate chambers (Plate 
84, fig. 2a) are mostly circular or broad-oval and 50-120 » in maximum diameter. 
The colour of both specimens in spirit is greenish brown. 
The skeleton. The poreless parts of the surface and the strands forming 
the pore-sieve nets are, both on the dermal and the gastral face, covered by 
a dense pinule-fur (Plate 83, figs. 45b, 61, 62). Under the poreless tracts of 
both faces paratangential, more or less centrotyle amphioxes and the lateral 
rays of pentactine megascleres form a superficial (hypodermal, hypogastral) 
skeleton. The strands of the dermal pore-sieve nets are supported by the 
lateral rays of hypodermal pentactines and a few centrotyle amphioxes (Plate 
83, fig. 62). The centra of the pentactines are here usually about 700 » apart. 
In the gastral pore-sieve nets no pentactines have been found. Here centrotyle 
amphioxes, congregated in dense bundles, alone occupy and support the strands 
of the reticulation (Plate 83, fig. 61). 
Numerous centrotyle amphioxes, rather scarce hexactine megascleres, 
and masses of microhexactines occur in the choanosome. Some of the micro- 
hexactines have straight, others curved rays. I think it not improbable that 
the former, which are much the scarcer, line the walls of the wide main canals, 
and are to be considered as canalaria; while the latter are imbedded in the 
choanosomal tissue, and are to be considered as parenchymalia. 
Four kinds of amphidiscs can be distinguished: — large and small macram- 
phidises, and large and small micramphidises. The large macramphidises are 
rather scarce in both specimens and confined to the choanosome, where they 
appear to be irregularly scattered. The small macramphidises are very numer- 
ous on and in the gastral membrane of specimen a, where most of those seen 
in situ in the sections were found to lie between the distal rays of the pinules 
wholly outside the sponge, with their shafts vertical to the surface (Plate 83, 
fig. 45c), while only a few are scattered irregularly in the gastral membrane. 
On the dermal face of this specimen small macramphidiscs have also been 
observed, but they are here not nearly so numerous. In specimen } these amphi- 
dises are similarly situated but much less abundant. The large micramphidiscs 
are very rare in both specimens, the small very numerous in 6, but somewhat 
