120 Prof. P. M. Duncan on Spongiophagus Carteri. 
h, fragment of the fibre, lateral view; 2, the same, transverse 
section (diagrams). 
Fig. 2. The same, from 8.W. Australia. Fragment, natural size. a, 
lobule, magnified; 6, subdermal reticulation; c, dermal termina- 
tion of fibre. 
Fig. 3. Pigmental cells of the Ceratina. a, dark opaque purple ; 4, light- 
coloured pinkish brown. 
N.B. The opaque purple pigmental cells in this illustration 
are made generally dark for contrast, or as they appear under a 
low magnifying-power ; otherwise their elementary composition 
is similar to that of the light-coloured pinkish-brown ones, with 
the exception of the pigment. 
Fig. 4. Pigmental cells of Dysidea fragilis= Spongelia. 
Fig. 5. The same, elongated, ? muscular. 
Fxg. 6. Filaments of the trama in Chondrilla nucula and saeciformis ; ? fili- 
form cells. 
Fig. 7. Spongilla. Sponge-cells of the parenchyma containing fragments 
of carmine. a, carmine, after Metschnikoff (Zeitschrift f. wiss. 
Zooloyie, Bd. xxxii. Taf. xxi. fig. 4). 
Fig. 8. Stelletta aspera and Dercitus niger, pigmental cells of. a, nucleus ; 
b, granules. 
Fig. 9. Chondrilla sacciformis. Pigmental granules, in irregular groups 
as they occur, viz. without cell-definition. 
N.B. Figs. 3-9 inclusive are on the scale of 1-24th to 1- 
6000th inch. 
Fig. 10. Luffaria. Fragment of the fibre, to show the relative size of its 
component elements. a, granular axis; 6, horny lamine. 
Fig. 11. Aplysina fusca. Fragment of the fibre, to show the relative 
size of its component elements. a, granular axis, tubular, mem- 
branous; 6, horny lamine; c, transverse section; d, granular 
axis; e, horny lamine; f, fragment of granular axis, greatly 
magnified; g, transparent sarcode ; h, granules. 
Fig. 12. Ianthella. Fragment of the fibre, lateral view. a, granular 
axis; 6, horny laminee, chiefly composed of pigmental cells. 
Fig. 18. The same. Fragment of small fibre, lateral view. a, granular 
axis; 6, first horny lamina bearing a few pigmental cells. 
Fig. 14. The same. Transverse section of the fibre, showing the horny 
lamine and their pigmental cells edgewise. a, granular axis; 
b, horny lamine. 
N.B. Figs. 10-14 inclusively are all diagrams. 
Fig. 15. Dictyocylindrus laciniatus, Mauritius. a, abortive development 
of the spicule ; 0, cells of the parenchyma. (Scale the same as 
that of fig. 1, e, for analogical contrast.) 
XIV.—On an Organism which Penetrates and Excavates 
Siliceous Sponge-spicula (Spongiophagus Carteri). By 
Prof. P. Martin Duncan, F.R.S., Pres. Royal Microscop. 
Soc., &e. 
In a communication which I made to the Royal Microscopical 
Society on June 8, 1881, the presence of green-coloured cells 
on siliceous sponge-spicula, in relation to minute penetrations 
into their axial canals, was asserted. The occurrence of a 
