6 
AUSTRALASIAN ANTARCTIC EXPEDITION. 
the position of the nuclei of the collared cells, which are in the long-drawn-out condition 
characteristic of asphyxiated calcarea (examined in R.N. T 10). 
The skeleton arrangement and spiculation are very typical. The following 
description of the spicules is taken from R.N. Til. 
Spicules :— 
(1) Triradiates (fig. 6a); with wide oral angle, frequently approaching 180°; rays 
approximately straight, fairly stout, fairly gradually and sharply pointed; 
paired rays commonly measuring about 0-098 by 0-009 mm. when fully 
grown; basal ray usually shorter to a varying extent and often more slender. 
(2) Quadriradiates (figs. 6 b, 6c); similar to the triradiates but with the addition of 
an apical ray, which is moderately well developed, fairly stout but not very 
long, sharply pointed and commonly gently curved. 
(3) Oxea (figs. Qd, 6e). There is only one kind of oxeote or monaxon spicule 
present, though they vary considerably in size, some of them being small enough to be 
classed as “ microxea.” The spicule is considerably flattened and slightly curved in 
the plane of the flattening (fig. 6d). It is fairly gradually and sharply pointed at the 
proximal end, which is apt to be bent somewhat sharply to one side in a plane at right 
angles to the flattening (fig. 6e). The distal end is hastate, sharply marked off from 
the remainder of the spicule by a slight annular thickening situate at about one-twelfth 
of the length of the spicule from the extremity. A typical example measured about 
0-14 by 0-006 mm. A smaller specimen measured 0-09 by 0-005 mm. The largest I 
have seen measured only 0-17 mm. in length. 
These monaxon spicules exhibit marked differences in shape and refringency 
according to the position in which they are viewed. When lying on edge (fig. 6e) they 
are narrower and much more highly refringent, the outlines appearing thicker and 
blacker than when lying flat (fig. (id). 
Professor Minchin, in his very elaborate memoir on “ The characters and 
synonymy of the British Species of Sponges of the genus Leucosolenia ” [1905], has. 
fallen into a very curious error with regard to these spicules, in which he has been 
followed by Jenkin [1908]. He says (op. cit., p. 359) : “ A remarkable point with 
reference to the monaxons of Leucosolenia, which I have found to hold good, not only 
with regard to the species described in this memoir, but also for all other species that 
I have examined, is that the monaxons can be separated more or less easily into two 
varieties, distinguished by the fact that one kind appears very refringent, the other, 
by comparison, pale, under the microscope. The refringent monaxons are always, 
scarcer than the pale ones, but their peculiar optical property makes it very easy to find 
them, especially under low powers (Zeiss, Oc. II, Obj. B). In form the two kinds of 
monaxons may not differ essentially, but the refringent ones always show certain 
characteristics which may be summed up by saying that they tend to be straighter, 
more slender, and sharper than the others, and their distal barb is less distinct or absent,”' 
