134 ARTHUR DENDY. 
c. The Canal System. 
The canal system of Lelapia australis conforms iu all 
respects to the typical Leuconoid arrangement, the entire 
sponge being, as already pointed out, a single Leuconoid in- 
dividual. The flagellated chambers are spherical or ovoid, 
only about 0:06 mm. in diameter and frequently less. They 
are thickly scattered in the transparent, gelatinous, meso- 
dermal ground-substance which separates the branches of the 
inhalant and exhalant canals. Their exhalant openings are, as 
usual, circular and well-defined, each with a delicate chamber- 
diaphragm. The prosopyles, which are not very easy to make 
out in small Leuconoid chambers, I have not succeeded in de- 
tecting. 
The inhalant canal system is irregular and more or less 
lacunar. Owing to the feeble development of the dermal 
cortex, there is no separately recognisable cortical canal 
system. The inhalant pores are small and scattered over the 
dermal surface. They open into short canals which unite to 
form larger trunks before penetrating the deeper parts of the 
sponge-wall, but there appears to be nothing definite about 
the arrangement. The smaller exhalant canals collect into 
large trunks, which run to open on the gastral surface, pierc- 
ing the gastral cortex more or less at right angles. The wider 
parts of these trunks are lined by a layer of laterally extended 
sagittal triradiates, similar to those of the gastral cortex, and 
amongst them may be seen sagittal triradiates like the sub- 
gastrals, with long basal rays projecting into the surrounding 
tissue at right angles to the course of the canal. These facts 
argue in favour of the supposition that the larger exhalant 
canals in Lelapia may be formed by pitting in or folding of 
the gastral surface. The openings of the exhalant canals (fig. 
6, ex. ap.) into the wide gastral cavity are abundantly scattered 
over the inner surface of the gastral cortex, and are provided 
with membranous diaphragms, as Mr. Carter has already 
pointed out. From .the gastral cavity, of course, the water 
