BIOLOGY. 
Bpong. 5 
b. Canal- system [cf. Titles 20, 21]. 
Lendenfeld (21) finds the inhalant pores of Tethya situated on the 
sides of the inverted cones which protrude from the surface. In Placo- 
spongia these pores are confined to the bandshaped zones free from 
rseudosterrasters, that separate the superficial armour-plates from each 
other. In Vioa , Papillella and Latrunculia they are situated on the 
summits of the papillae. In Vioa they sometimes form a ring round an 
osculum. In certain free forms of Vioa viridis ( Osculina polystomella , 
0. Schmidt) the poregroups are, like the oscules, surrounded by serrated 
lips. In the cortex of his new Cinachyra voeltzkowi , Lendenfeld (20) has 
found the same ovoid cavities with perforated walls which Sollas had 
previously described in Cinachyra barhata. According to Sollas, there 
are no other pores than the pores in the walls of these cavities, whilst 
Lendenfeld found pores also on the exposed parts of the surface. He 
therefore does not consider (as Sollas had done) the ovoid cavities as partly 
belonging to the inhalant system, but assumes that all these cavities 
belong to the exhalant system and that the pores on the exposed parts 
are the inhalants. 
Lendenfeld (21) finds the inhalant canals of Vioa , Papillella and 
Tethya just below the surface narrow and slit-like. The Yioas and 
Papillellas are traversed by wide, branching canals which probably 
anastomise and in some forms have a vestibular character: inhalant 
canals arising from them and oscular apertures opening out into them. 
In Vioa ramosa these canals attain a width of 4 mm. 
The ciliated chambers of Clavulina are, according to Lendenfeld (21) 
mostly spherical and 0 02 — 0 05 mm. in diameter. The smallest chambers 
are those of the Snberitidce. 
The oscular tubes of Astromimus luteus pervade, according to Lenden- 
feld (21), the whole of the massive Sponge in the shape of straight and 
wide vertical canals. Thoy are very numerous and run closo together, 
side by side. The oscules of several species of Vioa and Papillella are 
covered with sievemembranes and surrounded by serrated lips. 
c. Skeleton [cf. Titles 6, 14, 20, 21, 34, 35]. 
According to Doderlein (6) the skeleton of Petrostroma schulzei is 
composed of a firm network and of free spicules, both of carbonate of lime. 
The network is structurally and genetically similar to the network of 
siliceous rods forming the skeleton of the Dictyonine Hexactinellids. It 
consists of stout triactines firmly cemented together by carbonate of 
lime. During the cementing process the shape of these triactines is 
entirely lost. Herein Petrostroma differs from the fossil Pharetrones. 
Among the free spicules the two-pronged forks — they are triactines — 
which form bundles are particularly interesting as occurring only in 
Petrostroma , Lelapia and the Pharetrones. 
In spite of the fact that sometimes, as for instance in Asteropus 
incrustans and Vioa vastifica , so many spicules of all transitional dimensions 
are met with, that no sharp limit can be drawn between the Megascleres 
and the microscleres, Lendenfeld (21) thinks that this distinction should 
be upheld. It shows however that there is no real, qualitative, difference 
between the large (megascleres) and the small (microscleres) spicules of 
siliceous sponges. 
F. E. Schulze (35) draws attention to the fact that tho shapo of somo 
Hexactinellid spicules indicates certain relations to crystals of the regular 
system. Thus the Discoctaster-rays of Acanthascus and Rhabdocalyptus 
mark the positions of the corners of a cube ; the oblique connecting rods at 
the joining-points of the dictyonal network of Aulocystis etc. represent 
