CALCAREOUS SPONGES—DENDY. 
7 
&c. As regards refringency, he concludes “ that the difference between the two types 
is due to a difference in the rotation of the axis of crystallization to the form of 
the spicule.” 
It seems almost incredible that so careful an observer as Professor Minch in should 
have fallen into so simple a trap. It never seems to have occurred to him that he was 
merely looking at the same spicule in two different positions. The mistake is just the 
same that Bowerbank made many years ago with regard to his “ bi-dentate ” and 
“ tri-dentate anchorates,” and is the more surprising in that the triradiates and quadri- 
radiates of Leucosolenia show exactly the same difference in refringency according to 
whether they are viewed flat or edgewise, as do the monaxons. 
To any one who has seen these monaxon spicules and performed the simple 
experiment of rolling one over under the microscope, as I have done, observing how 
the form and the refringency change according to the position of the spicule, it must 
seem hardly necessary to give further proof of the correctness of this explanation of the 
supposed existence of two kinds of monaxons in species of Leucosolenia. I would 
point out, however, that everything which Professor Minchin himself says on the subject 
supports this conclusion. Their occurrence in all species examined by him* is in itself 
extremely suggestive, so also is the fact that the “ refringent ” individuals are less 
numerous than the “ pale ” ones, for it is less likely that the spicule will he on its edge 
than that it will lie flat. The differences in shape are also just such as would be expected. 
A precisely similar condition is seen in the microxea of Leucetta macquariensis, described 
in this report (c/. figs 8c, 8 d), and in the oxea of Grantia tenuis also found in the collection. 
Leucosolenia botryoides var. macquariensis approaches more nearly in its characters 
to Leucosolenia variabilis than to the typical European form of A. botryoides as described 
by Minchin (op. cit.), while perhaps differing from both in the very strong development 
of the basal network of tubes and the relative shortness and scarcity of the oscular 
tubes. 
Minchin himself points out that the difference between L. variabilis and L. botryoides 
is “ purely one of degree in every respect,” and I prefer to follow those authorities who 
consider L. variabilis as a mere variety of L. botryoides. It is interesting to find a variety 
of this common European species in so remote a locality as the Macquarie Islands. 
Register Nos., Locality, &c .—I. 10-13. Macquarie Island. Picked up on beaches 
after storm, West Coast. 
Leucosolenia ventricosa (Carter). 
Clathrina ventricosa Carter [1886]. 
Leucosolenia ventricosa Dendy [1891]. 
Leucosolenia ventricosa Dendy and Row [1913]. 
Several specimens of this common and easily recognisable species occur in the 
collection. It is unnecessary to add anything to the full description which I gave in 
* Although he himself points out this fact Minchin nevertheless actually gives the presence of the supposed two kinds 
of monaxse as a diagnostic character of Leucosolenia variable. 
