GENERAL ANATOMY AND PHYSIOLOGY, FOSSIL SPONGES. SpOUg. 20 
chambers constitute a unilaminar zone between the exhalant and inhalant 
canals ; thus the outer surface of the Sponge and the surface of the 
exhalant canals represent the outside of such a sac, while the ciliated 
chambers and the inhalant canals represent its inner wall. 
Kent, (6) p. 167, pi. viii. figs. 19-21, finds that the detached collar- 
cells of Sponges, when again brought into contact with the Sponge, throw 
out a film of cytoblastema around them. 
Structures resembling those which other authors have termed sperm 
capsules and spermatozoa are figured by Kent, (6) pi. x. figs. 12, 13, & 
16-18, as sporo-like bodies and sporocysts in Ilalichondria ^md Hymeni- 
acidon ; similar bodies are also described as spores, &c., from Leiico- 
solenia coriacea and other calcareous as well as silicious Sponges, 1. c. p. 173. 
They are stated to be derived in some cases from the splitting up of collar- 
cells, and to develop into collar-cells again ; their spermatic nature is 
denied. 
Marshall, (7) p. 117, concludes that the arrangement of the skeleton 
of all Sponges is regulated by the course of its water- canals, and dis- 
cusses this method of its production, p. 96. It is doubtful whether all 
horny fibres have an outer coat. 
‘Trichites,’ term applied by Sollas, (12) p. 133, to sheaves of hair-like 
spicules in Stelletta normani ; ‘Chones,’ ‘Chona3,’ or ‘cortical funnels,’ terms 
applied to the intermarginal cavities of Bowerbank by the same authoi’f 
1. c. p. 135, &c. Cf. also under Stelletta normaniy sp. n., and Geodia 
harretti, supra. The synonymy of the names of the different structures 
of the dermal layer also given, 1. c. p. 141. 
Essential difference between vesicular incurrent canals in Geodina and 
the racemose type of excurrent canals in the Leucones, maintained by 
the same author, 1. c. p. 406. 
The Sponges Psammascus, Dysidea^ P sammoclema, according to Mar- 
shall, (7) p. 121, appear to take a passive, Psammopemma an active, 
part in the process of appropriation of foreign bodies. 
S. O. Ridley, J. L. S. xv. p. 149, gives an account of two cases in 
which the spicules of a recognizable species of siliceous Sponge had been 
incorporated with the skeletons of other species of siliceous Sponges 
which had grown near it. 
Proportions of the different kinds of foreign bodies in various Psam- 
monematous Sponges given by Marshall (7). 
For pathological changes in Sponges produced by presence of foreign 
organisms, see Sollas, (12) pp. 263 & 407. 
Fossil Sponges, Chief Works on. 
14. Carter, H. J. On Fossil Sponge-spicules from the Carboniferous 
Strata of Ben Bulben, near Sligo. Ann. N. H. (5) vi. p. 209, pi. xiv.B, 
figs. 1-17. 
15. Hinde, G. j. Fossil Sponge-spicules from the Upper Chalk. 
Munich ; 1880, 8vo, 5 pis. 
An account of the sponge-spicules contained in the interior of a single 
