16 Spoilg. 
XVII. SPONGIflE. 
a rod or rhabdus, and the concretions figured by Maas are abnormal 
formations ; Weltner (62), pp. 190-193. 
Sandgrains, etc. in spongin fibres ; they penetrate from the exterior 
through the skin of the sponge ; Seurat (52), p. 261. A careful study of 
the fibres of Arenochalina mirabilis leads to the conclusion that the main 
fibres do not take in sandgrains at their apices, as supposed by Minchin 
[(47) Zool. Bee. 1900, p. 42], but at any point of their surface and at a 
distance below the growing apex ; Whitelegge (65) pp. 213 & 214. 
(d) Skeletal Anatomy. —Skeletal anatomy of Euplectella , Ijima 
(29) pp. 43-57 : of Craticularia ; Malfatti (40) pp. 282-284 : of Spon- 
gilla; Kukenthal (34) pp. 40-42. 
[N.B. Details of the spiculation and skeletal anatomy of individual 
species, such as are found in every systematic description, are not recorded 
separately here.] 
(v) Histology. 
(a) General Accounts. —The old sarcode-theory of O. Schmidt 
and the syncytium-theory of Haeckel “ have preserved a certain degree of 
applicability” in the case of the dermal layer of Hexactinellids, p. 160.— 
General histological composition of Hexactinellid body-wall, p. 41 [cf. II, 
B, iii].—Summary of the histology of Euplectella marshalli , pp. 190-192 ; 
Ijima (29). 
Histology of Tethya ; Maas (38) p. 267 : of Spongilla (?) vasta, n. sp., 
p. 200 : of Spongilla sarasinorum , n. sp., p. 197 : and of Pachydictyum 
globosum, n. g. n. sp. of Spongillince , p. 189 ; Weltner (62) : of the Bath- 
sponge ; Seurat (52) pp. 259-261. 
(b) Histology of Special Organs or Classes of Cells. — 
Cell-outlines not demonstrable by special methods on either trabeculae or 
chamber-wall, p. 33.—Trabeculae and dermal membrane of Regadrella 
oJcinoseana , p. 247.—Structure of the trabeculae of Euplectella marshalli. 
The entire trabecular system consists of a network, or cobweb, of syncytial 
protoplasm, containing “free” nuclei, i.e. without cell-outlines around 
them. The “ trabecular cobweb ” is probably unstable in form, to a 
certain degree, during life, as the result of protoplasmic contractility. 
The trabeculae are not covered by a flat epithelium (pace Schulze), nor do 
they contain any intercellular matrix or mesoglcea , which is totally un¬ 
developed in Hexactinellida. The naked syncytial trabeculae “stand for 
the mesenchyme of other sponges” ; they represent “the primitive mother- 
tissue, from which both the connective tissue cells and the pinacocytes of 
other sponges have later differentiated themselves”; pp. 147-165 ; Ijima (29). 
Epithelial contractile elements in Tethya ; Maas (38) p. 267. 
Cellules spheruleuses of Gellius rudis , p. 14.—Collenchyma and cellules 
spheruleuses of Halisarca dujardini var. magellanica, p. 45 ; Topsent 
(60). 
Structure of the flagellated chambers and the choanocytes of Euplectella 
marshalli etc. The chambers in most Hexactinellids have the form of 
cups, thimbles, or glove-fingers, but in two species of Hyalonematidce 
they “are represented by an intercommunicating system of canals, whose 
wall consists of the membrana reticidaris .” Close to the rim of the apopyle 
each chamber is united to its fellows by a connecting membrane , often 
fenestrated, which, together with the walls of the chambers themselves, 
divides off the incurrent lacunae externally from the excurrent lacunae 
internally. The connecting membrane is continued inwards round the 
aperture of the apopyle as an iris-like marginal membrane ; both alike are 
parts of the trabecular system. The chamber-wall is constituted by the 
