ANATOMY AND PHYSIOLOGY. 
SpOVg. 1 3 
Protozoa and Metazoa, representing a colony of Protozoa, one half of the 
cells being nutritive and the other half locomotor and respiratory forms. 
The Sponges are a far lower branch of the Metazoa than the Codente- 
rata, owing to digestion being effected by them within internal cells as 
well as by those lining the alimentary canal. Metschntkoff, (7) p. 374. 
Thickness of Sponge-fibres as a guide to distinction of species, (9) 
p. 634, is only useful when applied to the connecting (or horizontal) fibres 
of washed-out skeletons ; the mean and maximum measurements are to 
be taken, not the minimum. 
The tendency of cylindrical spicules is to assume a globular form, (13) 
p. 50, that of acerates is to branch at the point. Spines of spined acerates 
of Plocamia not penetrated by axial canal ; 1. c. Resistance of certain 
spicules to action of potash on interior ; 1. c. Composition of residual 
membrane left by silicious Sponge-spicule, after treatment with acid, is 
doubtful ; 1. c. p. 51. Heads of axial spicules more generally eroded 
than their shafts ; 1. c. p. 52. 
Great variations observed by Marshall & Meyer, (6) p. 276, in the 
amount of spiculiu contained in siliceous spicules ; there is an abundance 
of it in the long axial spicules of Ilyalonema, but mere traces in Euplec- 
tella and Eurete. 
“ Spinispirula,” term applied to a form of spicule found in sundry 
Suberite Pachytragid and Pachastrellid Sponges, (1) pp. 301 & 355 ; the 
spinulo-multi-angulated cylindrical form of Bowerbank. 
“ Sceptrella,” (1) p. 358, term applied to the sceptre-like spicules of 
Podospongia loveni, Latruncula cratera, and other Suberitic Sponges ; 
it assumes different forms, and perhaps graduates into the spinispirula. 
Sponge spicules generally lose in length as they gain in thickness, and 
the maximum size varies with different specimens ; (1) p. 284. 
W. J. SoLLAS, Ann. N. H. (5) iii. p. 170, while correcting a statement 
in Ann. N. H. (5) ii. p. 359, about a Calcareous Sponge-spicule, mentions 
finding large free triradiate calcareous spicules with central canals en- 
larged by solution. Passage from spiculose horny fibre in Sponge, to a 
wholly spicular not-horny form is quite gradual, (13) p. 48. Close 
family relation between the different skeleton spicules of a Sponge, 
Plocamia, (13) p. 48, pi. vii,, shown by study of their varieties ; the 
dermal spicules giving origin on the one hand to the axial spicule and on 
the other to the young form of the acerate, and thence to the adult 
spined and non-spin ed acerate spicules. 
Variations from the typical form exhibited by four to five per cent, of 
the triradiate echihating spicules of a species of Sponge, (12) p. 19. They 
pass through uni-axial and quadriradiate forms. The characters of the 
central canal, however, show the former really to belong to a biradiate 
type ; and in general indicate in Sponges the true character of the. 
spicule, since it originates in the spicule-cell. 
The amoeboid character of the sponge cell is strongly insisted on in con- 
nection with the nutrition of Sponges, by H. J. Carter, Ann. N. H. (5) iv, 
p. 375. This may lead even to the retraction of the cilium of a ciliated 
cell, and its assumption of an amoeba-like form. The spongozoon does 
(J. c. p. 378) take in food; it also very likely has reproductive functions. 
