EEPOKT ON THE TETHACTINELLIDA. 
163 
specimens which came into my hands consisted simply of the broken-off excurrent 
tube — the same part of the sponge that served fof Mr. Eidley’s description of the 
species. On similar fragments of an allied species (from the description I can hardly 
suppose it to be the same) Marshall’s account of Agilardiella radiata was based. After 
making both longitudinal and transverse sections through the tube, I searched diligently 
in the prepared slices for flagellated chambers, and though at first surprised at not 
finding any in a specimen with evidently well-preserved tissues, I finally concluded that 
the tube was not the whole sponge, and that the part containing the choanosome was 
missing. Under this impression the figure of one of the cloacal tubes (PI. XVIII. fig. 2) 
was represented upside down, the conical disc having been regarded as a part of the 
cortex torn away from the sponge-body, while as we now know it really forms the free 
distal termination of the excurrent tube. All doubts as to the existence of a sponge-body 
were subsequently set at rest by a fragmentary specimen which I long afterwards 
received, and which is represented on PI. XVIII. fig. 3. Finally, when this Eeport 
was well-nigh concluded, a collection of almost perfect specimens came into my hands, 
showing not only the excurrent tube, but an incurrent conduit as well, a totally new 
and unexpected feature, and possibly unique amongst the sponges as a group. Unfor- 
tunately no specimen I have yet seen is complete from the beginning of the incurrent to 
the end of the excurrent tube ; in all, the excurrent tubes are broken off some distance 
apparently from the end ; on the other hand, numerous fragments of excurrent canals 
occur terminated by the conical disc, so that in fact aU parts of the sponge are known, 
and thus we are enabled to construct the restoration shown in PL XLI. fig. 2. 
A median longitudinal section of the sponge passing through both excurrent and 
incurrent tubes reveals the following structure (PI. XLI. fig. 3) : — In the sponge-body a 
central yellowish-grey opaque choanosome, surrounded by a translucent bluish-grey 
ectosome or cortex. In the centre of the choanosome is a dense white spicular nucleus 
from which spicular sheaves radiate towards the cortex and to both tubes ; at the base of 
the incurrent conduit they stop short, but those proceeding to the excurrent tube are 
continued into it, passing up its centre and along its sides to constitute the cloacal 
skeleton. The cortex is produced at each pole to form the outer wall of each tube. The 
excurrent canals of the excurrent tube can be traced into the choanosome of the sponge, 
where they ramify in the usual manner ; the single canal of the incurrent tube is sub- 
divided where it reaches the cortex into four large branches, which enter the cortex ; 
these are visible not only in sections, both longitudinal and transverse, but they can be 
traced like blue veins beneath the skin in whole specimens (PL XLI. fig. 2) ; after pro- 
ceeding some short distance they each bifurcate, and the diverging canals so produced 
again bifurcate, and finally subdivide into branches too small to be traced by a simple 
lens. Subsidiary canals are also given off above and below the main bifurcations. 
An examination of the superficial layer of the cortex failed to reveal the presence of 
