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Show 14 PROF. E. A. MINCHIN ON THE [May 2, all of small size. The big, spreading colonies of contortct always have monaxons. It is my belief that the absence of monaxons is simply a juvenile feature, so to speak, of the sponge, and that they are only formed when the sponge has grown to a certain size. Such changes of spiculation with age are probably more frequent in sponges than is usually supposed. For a parallel case I need only refer to Topsent's observations on Cliona celata. A point which requires brief discussion, however, is why Lendenfeld found only the spinosa-iorm in the Adriatic, and not the contorta-form, if these two forms are really only age-variations in one species. Are we to suppose that in the Adriatic the sponge does not acquire monaxons ? In my opinion the explanation of this point is to be sought in quite a different manner. In his ‘ Kalkschwamme der Adria ' [3] Lendenfeld describes another species of Clathrina occurring commonly in the Adriatic, namely C. reticulum. I have also found this species very abundant at Banyuls, and I possess many specimens of i t ; but my experience of this species at Banyuls differs sharply in one respect from Lendenfeld's observations upon it in the Adriatic. I find reticulum to be more constant in external form and characters than any other species of Ascon. All the specimens I have seen-and at one time I had some hundreds of specimens, collected in order to obtain the larval development-are compact, rounded, cushionlike masses of slender, closely-knit tubes, forming a dense and finely-meshed reticulum from which arise one or more oscular tubes of much larger calibre than the tubes forming the body of the sponge. I have figured such a specimen elsewhere (4, p. 6, fig. 6). In short I have never had the slightest difficulty in recognising reticulum at sight, though its spiculation often approaches that of contorta very closely. My astonishment was therefore great to find that Lendenfeld describes this sponge as occurring (at Sebenica and Lessina) in nearly all the forms generally found in Ascons. There is thus a great discrepancy between Len-denfeld's observations and mine with regard to this species, and I am inclined to think that this is to be explained simply by Lendenfeld not having recognised the true contorta, but having confused it with reticulum. This is a supposition which I am unable to prove or test; but if correct, it would explain why Lendenfeld did not find the true contorta occurring in the Adriatic as well as spinosa, and also why he finds reticulum so variable in form when in my experience it is so extremely constant. I may add, finally, that the figures of monaxons of reticulum given by Lendenfeld (3, pi. viii. figg. 7 e-7f ) are more like those of contorta than those of reticulum, though not exactly like those of either, as these sponges are known to me. I will now describe some of the historically important specimens to which I have had access, and I begin with the type-specimens of Bowerbank's Leucosolenia contorta in the British Museum (Bowerbank Coll. 988). The " type" consists of seven dried specimens, all very small, stuck on a card. The largest specimen |