STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 333 
neighbourhood of the oscular tube and containing each 
a single large embryo (e.). These cavities appear to be 
entirely closed and cut off from the remainder of the canal 
system of the Sponge, but it seems possible that they are really 
portions of the exhalant canal system, specially modified to 
serve as receptacles in which the embryos are lodged during a 
large portion of their development. There are two arguments 
in favour of this view : (1) The position of the cavities in 
question, in close proximity to the oscular tubes. (2) The 
well-known fact that in many Sponges the embryos normally 
escape from the parent through the exhalant cauals 1 . 
(f) General Remarks on the Canal System. 
From the foregoing account it will be evident that the canal 
system of Stelospongus flabellifor mis approaches most 
nearly to Dr. Vosmaer’s third type (18) ; although, however, 
several chambers communicate with one and the same ultimate 
inhalant or exhalant lacuna, the openings of the chambers are 
provided with short and relatively wide cameral canaliculi. 
Still the canal system differs little from the ordinary lacunar 
type so characteristic of the large family Halichondrina 
(14), and also found occasionally in the Clavulina (14) and 
other groups. 
With regard to other members of the Ceratosa, some have 
been shown to possess the lacunar type of canal system and 
some the canalicular type. Professor Schulze (15) has de- 
scribed both these conditions as they exist in different members 
of the group. Unfortunately, I am unable at present to obtain 
access to his original papers, but I may quote the following 
passage from Polejaeff's work (13) which will sufficiently indi- 
cate the state of the case : — “ Schulze ascertained, in fact, 
that while an Aplysina, and on the other hand a Eu- 
spongia or Cacospongia, are characterised, in the or- 
ganisation of their canal system, by comparatively small, 
round, or pear-shaped flagellated chambers, each possessing 
1 liidley and Dendy have figured an embryo escaping through an exhalant 
canal in Esperella Murrayi (14). 
