STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 129 
remarkably large. Vent single, terminal, represented by a 
narrow elliptical opening about + inch in its longest diameter, 
so constricted in the centre as to be closely approximated by 
an infolding of the lip on each side; provided with a peri- 
stome, whose spicules here are broken off short; leading intoa 
cloaca corresponding in shape with the specimen, that is, wide 
above, narrowed to a point below (after which the stem becomes 
solid).” 
The specimen thus described is obviously a single Leuconoid 
individual. The smaller specimen, however, as described by 
Mr. Carter, showed some indication of a tendency to branch, 
and possibly the species may sometimes form branching 
colonies. 
B. The Skeleton. 1. The Spicules. 
The following account of the spicules is taken from prepara- 
tions boiled out with caustic potash, as it is extremely difficult 
to obtain a satisfactory view of entire spicules in their natural 
position. I have not had the opportunity of examining the 
spicules of the peristome, but we learn from Mr. Carter’s 
writings that there is no important modification amongst 
these which is not also met with elsewhere. All three prin- 
cipal types of calcareous spicules are met with, but the 
quadriradiates are rare, and the apical ray is very feebly 
developed. 
Oxeote Spicules.—Three varieties may be clearly dis- 
tinguished : 
(1) Large, stout, fusiform; usually slightly curved and 
slightly irregular in diameter; tapering gradually to a sharp 
point at each end (fig. 2, a). Size variable, when fully grown 
about 1:9 by 0°11 mm. 
(2) Long, straight, and very slender, gradually and sharply 
pointed at both ends, and sometimes slightly hastate or 
bayonet-shaped (fig. 2, 4). Size variable, say about 0:9 by 
0:008 mm., but often less. 
(3) The so-called “ mortar-spicule.’ Minute; straight or 
slightly crooked ; gradually and sharply pointed at both ends, 
