REPORT ON THE TETRACTINELLIDA. 
xxxiii 
plane surface on which the excurrent canals open ; the openings of these canals for con- 
venience are called oscules, but they are really homologous with the mouths of derivative 
excurrent canals. 
The Oscules of Compound Sponges. — In compound sponges characterised by the 
presence of more than one evident oscule — and all simple sponges are liable to become 
compound — we may regard each oscule as indicating a separate system of canals and thus 
in a sense as a sign of individuality. The origin of additional individuals may be 
attributed to a process of budding or internal gemmation from some excurrent caual 
running near the surface of the sponge, close beneath the ectosome, and thus serving as 
a kind of internal stolon. 
The Pokes. 
These which are the immediate openings of the incurrent canals through the investing 
epithelium to the exterior are always very small, usualiy about 0'05 ram. in diameter, 
sometimes much less, 0'008 mm. in Psammastra murrayi, sometimes much more, 
0'32 mm. in Thenea ivy villi. They are either uniformly dispersed over the poriferous 
surface or collected in sieve-like groups, or they form the single openings of chones. 
Sometimes they are more numerous over special areas, or indeed restricted to them. 
. Since they naturally can only occur over the subdermal cavities or intercortical 
canals of the sponge, one would not expect to find them generally distributed, yet this 
does occasionally happen when the cavities immediately beneath the skin are of great 
superficial extent, e.g., in Caminus sphseroconia (PI. XXVII. fig. 2), but more usually 
even in such cases they are collected into sieves, of which numerous examples are described 
in the body of the Eeport (p. 143, PI. XV. fig. 20 ; p. 232, PI. XXII. fig. 14 ; PI. XXX. 
fig. 3). In the Geodiidse they commonly occur as sieves over the distal ends of the 
chones, the roofs of which may then be said to be crihriporal (PI. XL. fig. 4) ; but in 
some of the more specialised genera — Erylus (PI. XXVIII. fig. 17), Isoyis, — there is but 
a single pore to each chone ; in this case the poral roof may be distinguished as uniporal. 
The restriction of the pores to special vestibules occurs in the Tetillid genus Cinachyra 
(p. 27, PI. XXXIX. fig. 1); in the Stellettid Disyringa they are confined to an extension 
of the cortex, which forms a special incurrent tube (p. 163, PI. XLI. fig. 3); in other 
sponges, such as the Thenese, special poriferous recesses are present in addition to pores 
generally distributed. 
Lipogastrism and Lipostomy. 
In many sponges the oscules are not distinguishable from the pores (lipostomy), and 
iu some cases all traces of the paragastric cavity have also disappeared (lipogastry). 
(ZOOL. CHALL. EXP. — PART LXITI. — 1888.) RlT 6 
