R. W. H. ROW—REPORT ON THE SPONGES: CALCAREA. Wy 
optic axis of the spicule or ray, as it is impossible to imagine that the crystal 
components of an already formed spicule should change their position in the 
spicule as it turned, so as to retain the primitive orientation in the sponge of 
their optic axis. 
Thus the morphological movement of the spicule would not affect its 
orientation with regard to the optic axis, though it is very possible that the 
morphological movement might tend to influence the physical orientation of 
the calcite, which quite possibly might continue to be laid down in its 
primitive orientation with regard to the sponge rather than with regard to 
the spicule. 
From a polariscopic examizetion of the actual prochiacts and secondary 
triradiates, it appears that the orientation of the spicule about its optic axis 
varies very greatly, but whether these variations are related in any manner 
to the morphological characters of the spicule, or to the amount of the 
widening of the primitive oral angle, I am unable to say. 
In connection with the morphologically secondary sagittal triradiates of 
Grantilla and the entire replacement in this genus of the primitive articulate 
tubar skeleton by such spicules or by prochiacts, it is noteworthy that, 
leaving out of account Megapogon, which has a leuconoid canal-system and 
an irregular spicule arrangement, there are but two genera in the families 
Chiphoridze and Staurorrhaphidee which retain their articulate tubar skeleton. 
In Streptoconus the chiactines form the gastral joint of the articulate tubar 
skeleton, the upper joints being composed of typical sagittal triradiates. 
In Grantiopsis the tubar skeleton, save in so far as the chiactines are 
concerned, is composed of triradiates which have undergone a considerable 
modification, the paired rays of the spicule having almost disappeared, and 
being only represented by minute projections at the gastral end of the spicule. 
In all the other genera of these two families the tubar skeleton is entirely 
composed of the chiactines, with in some species the very occasional addition 
of a triradiate, presumably from its position a remnant of the articulate tubar 
skeleton. 
A similar replacement occurs in the Heteropide by means of subdermal 
and subgastral secondary sagittal triradiates. Very frequently in this family 
again the loss of the primitive tubar spiculation is complete, in which case 
there is formed an inarticulate tubar skeleton. As typical examples of this 
may be mentioned Grantessa stauridea and Grantessa simplea. 
Among the syconoid Amphoriscidee the replacement of the tubar skeleton 
is characteristically by large quadriradiates and triradiates. In Amphoriscus 
and Syculmzs, for example, there are present subdermal and subgastral quadri- 
radiates whose apical rays point respectively gastral- and dermalwards, while 
in Heteropegma the former alone are present. In all these forms the spicules 
of the articulate tubar skeleton are very considerably reduced, the reduction 
in size being very especially noticeable in some species of Heteropegma. 
LINN. JOURN.—ZOOLOGY, VOL. XXXI. 16 
