REPORT ON THE TETRACTINELLIDA. 
11 
cladi O'l by 0'0237, cbord O'l mm.; cladal end of rhabdome 0'021 mm. long, the axial 
fibre of the rhabdome extending into it 0’079 mm. 
II. Microsclere. 6. Sigmaspire of the usual form; O'OllS mm. long. 
In young specimens the spicules are smaller, in correspondence with their size ; thus, 
in an individual measuring 18 and 13 mm. along two diameters, the oxea is only 3 ’5 
mm. long ; in another, 32 and 26 mm. in diameter, it is 4 '6 5 mm. long. 
Colour , — White to yellowish-grey. 
Hahitat. — Kerguelen, 10 to 100 fathoms. 
Station 149b, off Eoyal Sound, Kerguelen, January 17, 1874; lat. 49° 28' S., long. 
70° 30' E.; depth, 25 fathoms; bottom, volcanic mud. 
Remarhs . — About fifty specimens of this fine sponge were brought from Kergueleu, 
where they grow in company with Cinachyra harhata. The largest is 1 30 mm. high, 
and 75 mm. in diameter, but is without roots. One specimen, 92 mm. high and 70 mm. 
in diameter, stands on a basal mass 32 mm. high and of about the same diameter as the 
sponge. 
In its youngest state, as represented by a specimen 8 mm. in diameter, the sponge is 
nearly spherical (PI. V. fig. 4) ; it soon becomes egg-shaped, and the narrow end is 
produced into anchoring tufts, which as it increases in size very soon agglomerate into 
wool-like clots ; and by the time the sponge has reached a height of 25 mm. it is pro- 
vided with the characteristic basal mass. 
The ectosome is about 0‘3 to 0'8 mm. thick ; it consists of fibro- vesicular collenchyma, 
the vesicles being more numerous in the outer, and the fibres in the inner part of the layer. 
Just below the epidermis the vesicles are comparatively small and filled with faintly 
stained protoplasm, enclosing an oval nucleus with its nucleolus. Deeper towards the 
interior the vesicles are much larger, 0'0276 by 0'0395 mm., and the included nucleus, 
surrounded by a thin film of protoplasm, lies at some distance from the walls, with which 
it is connected by thin protoplasmic strands. In the larger cavities the remains of 
several cells usually occur (PI. V. fig. 5), but they disappear subsequently, so that in the 
largest cavities no trace of cells may occur. 
The ectosome is not sharply marked off from the choanosome ; the appearance of 
flagellated chambers in the latter is the only certain sign by which it can be distinguished. 
The flagellated chambers differ considerably in size amongst themselves, the larger 
ranging from 0‘032 to 0‘044 mm. in diameter. They are eurypylous, the prosopyle 
measures about 0'0125 mm. in diameter, the apopyle from 0*02 to 0'03 mm. in diameter. 
Around the margin of the apopyle two or three sigmaspires are frequently embedded ; 
and a nucleus with granular protoplasm sometimes lies on one side, the protoplasm 
apparently extending around the margin, the whole suggestively like a single bounding 
myocyte. 
