REPORT ON THE TETRACTINELLIDA. 
xli 
Granular cells somewhat resembling the chromatocytes of Craniella carteri, and 
occurring both in isolation and in rounded aggregates, are characteristic of most species of 
Pilochrota (p. 125, PL XX. figs. 9, 11, 13 ; p. 130, PI. XIY. fig. 15 ; p. 132, PI. XIV. 
fig. 37 ; p. 133, PL XIV. fig. 21 ; p. 122, PL XXXIX. figs. 24-26). The function of 
these cells is unknown, but they have much the appearance of being pigment-cells without 
pigment. In Pilochrota gigas they occur in the fibrous processes by which the sponge 
attaches itself to foreign bodies, frequently running in rows between the fusiform cells 
of the fibrous tissue, and then reminding one of the appearance of fat- cells in some 
longitudinal sections of muscle in the higher animals. Granule-cells of unknown 
function also occur in Pcecillastra schulzii (p. 81, PL IX. fig. 29). 
In many species of Myriastra and Anthastra oval clusters resembling pigment-cells 
occur, but are really as I imagine groups of some Bacterial organism [vide PL XII. 
fig. 25). 
Inocytes. — Fusiform connective-tissue cells or inocytes were first described as muscle- 
ceUs in my account of Dragmastra (Stelletta) normani,^ but discovering that this was 
an error I pointed out their true nature in a succeeding paper on Geodia harretti. 
They may be most readily studied in fresh specimens of Tethya lyncurium (in which 
they form the densely fibrous inner half of the cortex), by treatment with gold chloride 
and formic acid, subsequent dissociation in 30 per cent, alcohol, and staining with borax 
carmine. 
When teased out they present themselves, as described in my account of Dragmastra 
normani, as long, fusiform cells, consisting of a clear, transparent, outer wall, which does 
not stain with reagents and readily splits on teasing into fibrillse, and a long axial thread 
which is fusiform, homogeneous, faintly bluish in colour, and highly refringent. Acetic 
acid renders the axial thread somewhat more distinct, nitric acid acts in the same way, 
but more vigorously ; caustic potash in a 5 per cent, solution causes the cell to swell up 
and renders the axial thread invisible ; strong nitric acid applied to the fibrous tissue 
destroys the outlines of the individual cells, producing an apparently homogeneous 
matrix, in which the axial threads remain sharply defined ; on adding magenta the 
latter stain deeply, but not the matrix. 
The axial thread bears much the same relations to the hyaline sheath that a 
collencyte does to the surrounding gelatinous matrix ; and though apparently structure- 
less in Stelletta normani, in Tethya lyncurium it always presents a finely granular 
character, and encloses in the middle a small oval nucleus, with the long axis lying 
in the same direction as that of the thread ; within the nucleus is a small spherical 
nucleolus. 
The inocytes are arranged with overlapping ends in parallel rows forming fibrous 
strands, these run parallel along the sides of the spicular fibres, along the course of the 
^ Ann. and Mag. Nat. Hist., ser. 5, vol. v. p. 136, 
(ZOOL. CHALL. EXP. — PART LXIII. — 1888 .) 
Err/ 
