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Show 1905.] SPONGE CLATHRINA CONTORTA. 11 monaxon or an abnormal triradiate (text-fig. 3, 3 f ) ; probably it is both ! My friend Mr. Alford has also found, in the slide of Topsent 12 e, four abnormal monaxons which have additional rays growing out laterally and thus become triradiates (text-fig. 6, 9 «-9 c). In one of these (9 b) the three rays are approximately equal in size and meet at the angles of an ordinary triradiate. For all these reasons I consider there is much to be said for regarding the monaxons of contorta as secondary monaxons derived from a triradiate system by suppression of one ray and hypertrophy of the two remaining, which become placed in the same straight line, or nearly so. The numerical variation in the monaxons is not less remarkable. In some specimens scarcely any monaxons are to be found ; in others they are extremely abundant. Thus in a specimen recently examined by me, I took a fairly large piece of the sponge, separated the spicules with Eau de Javelle, and mounted all I could get up with the pipette, covering three slides. After prolonged searching I found five monaxons to many thousands of triradiate systems. In another specimen in which I could find no monaxons, Mr. Alford by careful searching found two. It is often extremely difficult to be certain if a specimen has monaxons or not. Mr. Alford has kindly undertaken for me the task of counting the numbers of each kind of spicule found in different specimens, with the following results :- ' Triradiates. Quadriradiates. Monaxons. Kind of Monaxons observed. Total of Specimen. Actual number counted. Percentage of whole. Actual number counted. Percentage of whole. Actual number counted. Percentage of whole. 3 kinds of Spicules. No. 1 ) (z 3 ct-3 h). ) 93 3-278 + 2727 96-123 + 17 "599 + Large. 2837 No. 2 \ (Z 2 « -2 h). 5 No. 3 ........ 311 386 8-304 + 12-512 + 3423 2658 91-402 86-158 + 11 41 •294 + 1-329 + Large. Very large. 3745 3085 No. 4 ) (Plate I. B). ) No. 5 ........ 247 146 5-835 + 5-144 + 3965 2686 93-668 + 94'644 + 21 6 •496 + •211 + Very large. Gigantic. 4233 2838 No. 6 } (Topsent > 12 e). ) 267 10-349 + 2188 84-806 + 125 4-844 Gigantic. 2580 Total for } Species. ) 1450 7-506 17647 9135 221 1 1 4 4 19318 These results were obtained in the following way :-" Each specimen was put into Eau de Javelle to separate the spicules, and after careful washing, and being allowed to stand for some |