Structure of Marine Sponges. 337 
may be easily mistaken. Up to this time, however, I have 
only found this spicular element to exist in the shape of two 
forms of globular crystalloids of carbonate of lime covered 
with points similar to some of the siliceous spherical stellate 
bodies of Geodia arabica (Annals, vol. iv. July 1869, pi. 1. 
fig. 13 a)—not of the globular crystalloids of the crust, which 
all have a depression in one part of their surface. Such a de- 
pression does not appear to exist in the radiated globular 
erystalloids (spicules) of the compound Tunicata. 
Hence it seems to me that the Sponges are just as much a 
step to the Polyzoa and Tunicata as to the Corals, if not more so. 
pores of Corals, the part they play “is unfortunately still as 
good as unknown.” 
One does not assume that the inhalant pores of Sponges 
may not be in part respiratory organs, but that, unlike the 
Corals, they serve the purpose also of sifting the nutritive ma- 
terial which is drawn in through them by the internal organs 
of the sponge—in short, that, as in the Tunicata and Polyzoa, 
the respiratory water and the food enter the body through one 
aperture and come out at another. 
I have stated that there is only one vent in the young Spon- 
gilla grown from the seed-like body ; but sometimes (see my 
“ Ultimate Structure of Spongilla,” op. cit. l. c. p. 31) “ it hap- 
p that one of the large branches of the efferent system 
ursts and gives rise to an efferent current before the tubular 
Ann. & Mag. N. Hist. Ser. 4. Vol. vi. 22 
