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Show 12 PROF. E. A. MINCHIN ON THE [May 2, considerable time after each washing, the spicules were transferred to the slides by means of a pipette. . 1 " Each slide, when ready, then had marked upon its under surface twenty circular areas, each being brought into the microscopic field in turn and all spicules in each area carefully counted. When all the spicules were counted the circle was erased and the next circular area dealt with. " The counting was done with the aid of a camera lucida and three differently coloured crayons, thus ensuring that all spicules were counted and counted once only. " Each quadriradiate spicule had a number in blue marked upon i t ; the triradiate spicules were marked with successive red numbers and a green number noted a monaxon. At each counting a check could be made, and the counting was complete when each spicule was seen to have one number of a special colour upon it." The spiculation of Clathrina contorta thus shows, on the one hand, comparatively slight variation in the triradiate systems, and, on the other hand, extraordinary differences in number and size of the monaxons in different specimens. The variability is so marked, and the monaxons are frequently so difficult to find, as to suggest at once a possible extreme of variation in which the monaxons would be totally absent. Were this to occur we should have a variety of the sponge characterised by a type of spiculation which would lead to its being placed, in many current systems of classification, in a genus distinct from the variety in which monaxons occur. As a matter of fact, I may state at once that the variety of contorta in which monaxons are completely lacking is very common, and it has been described by Lendenfeld from the Adriatic under the name of Ascetta spinosa. This is no mere surmise on my part; I have been able to examine, in the collection of Canon Norman, a slide obtained by him from Lendenfeld, and bearing in Len-denfeld's handwriting the label " Ascetta spinosa." Text-fig. 4, 5 a -5 h, represents some spicules drawn by me from this slide. As will be seen, the spiculation differs in no single particular from that of the true contorta, except for the lack of monaxons. Since the preparation consists of tubes of the sponge mounted whole, it was not possible to obtain profile views of the gastral rays, except at the torn ends of the tubes, and in no case was I able to see an unbroken gastral ray in side view, but the fragments which I have drawn (5 f -5 h) are sufficient to prove that the gastral rays of this specimen attain the degree of length and slenderness characteristic of the species. Lendenfeld's specimen is, in fact, identical in character with other specimens of " spinosa " which I have from Banyuls (text-fig. 4, 6 a-6 g), and these again differ in no respect from the true contorta except for the absence of monaxon spicules. If Ascetta spinosa Lend, is to be regarded, as I believe, merely as a variety of Ascandra contorta, H., how is this variation to be explained ? The specimens of spinosa that have come under my notice agree perfectly in external characters with contorta, but are |