ANATOMY, EMBRYOLOGY, PHYSIOLOGY, BIOLOGY. SpOlig. 11 
less, except in the new genus Damiria. In this family appear fibrous 
tracts of spicules quite imbedded in spongin. Monaxon spicules pre- 
vail amongst the Oligoceratina , but various kinds of asters also occur. 
In Chonclrosidce the siliceous structures degenerate till they vanish, but in 
Placospongidce they are increased both in number and variety. The 
extreme of skeletal development is the differentiation into a cortical and 
an axial portion. A cortex appears frequently in Rent evince , and has 
been inherited from them by the Chalinince. Radially-disposed bundles 
of spicules often occur, especially in Tethyailce , where they arise from a 
central nucleus. This arrangement is homologous with the similar ono 
of Tetractinellida. 
The canal system of the Oligoceratina is mostly of the third type. 
Microscopic dermal pores lead into subdermal spaces. In the thin-walled 
tubular Renierince the inhalant canals are distinctly radially arranged. 
In these forms pronounced lipostomy is the rule. In more modified forms 
the canal system is of the fourth type. Placospongia has immense sub- 
dermal spaces. These forms are seldom tubular, an exception being 
Subcrites mastoid eus, which is tubular, with a wide gastral space, and 
often in addition a pseudosculum and pscudogaster. 
The author concludes that the Oligoceratine Monactinellidai have 
arisen from Tetractinellid ancestors, probably Tetillhlce. From this 
family arose the Tcthyopsillidce , and from them the Tethyadce. From 
the Tethyadce is given off a branch, the Cliondrosida ?, in which the 
spicules degenerate, but the main stem continues from the Tethyadce into 
the Spirastrellidce aud Suberilidce. The Rcnicridcc are probably derived 
from Subcritidce , and have given rise to the Chalinidce. The Spongillidce 
are polyphyletic, and arise partly from Renieridce, partly from Chalinidce. 
Thus from the Tetillhlce can be traced a continuous series up to the Horny 
Sponges, with a continual tendency to degeneration, first of the tetraxon 
spicules, which become monaxon, and then are gradually replaced by 
spongin ; and, finally, the spongin fibres also degenerate, as in Hali- 
sarcidce. For description of the anatomy of Tethya seychellensis, Soli., 
see p. 330. 
In Tetractinellida spongin occurs, though rare. In Stelletta siemensi 
it occurs as numerous spherical or elliptical bodies of an intense brown 
colour, which are very resistant to acids and alkalis, but slowly dissolve 
in hot potash. They lie in closed follicles lined by cubical cells. The 
third type of canal system preponderates in the more delicate forms of 
Choristida , but in massive forms the fourth type prevails. In Lithistida 
the canal system appears to be of the third type. The canal system 
shows a certain resemblance to that of Aplysillidcc and Ilexactinellidce. 
Between the cortex and the region of the chambers is a zone of lacunes 
without chambers. Nothing was observed of a “ Sollas’s membrane.” 
For a description of the pores, pore sieves, pore calyces, chones, and sub- 
dermal spaces, see p. 334. 
In conclusion, the author describes the influence of vertical distribution 
upon the mechanical construction of the Sponge body. In abyssal 
