20 ON THE SPONGE CLATHRINA CONTORTA. [May 2, 



a primaiy monaxon spicule, derived from a single mother-cell, 

 and developing exactly in the same way as a single ray in a tri- 

 radiate system, with which it is strictly homologous. It may be, 

 on the other hand, a secondary monaxon, derived by modification of 

 an entire triradiate system by loss of one ray, perhaps in some cases 

 two rays. Good examples of monaxons undoubtedly of secondary 

 nature are the elbowed monaxons in the stalk of Clathrina lacunosco 

 Johnston (renamed Ascandra angulala by Lendenfeld). I believe 

 also, as stated above, that the monaxons of contorta are to be regarded 

 as secondary. It is clear that a character which is sometimes one 

 thing, in other cases quite another thing, cannot be usefully 

 employed for purposes of systematic classification, not, at least, 

 until more is known about it. 



If Ascetta spinosa be put as a synonym of Clathrina contorta, 

 it is seen that the species has a w^de range, extending from the 

 Adriatic round the coasts of France into the English Channel, and 

 probably also on to the coasts of Great Britain. 



It is my pleasant duty finally to express my thanks to friends who 

 have assisted me in the preparation of this memoir, put together 

 from observations for the most part of long standing, at a time 

 when the stress of other work, caused by preparations for my 

 departure for the Tropics, was very great. My friend Mr. G. R. 

 Alford, who is making a special study of the variation of this 

 sponge, has given me valuable assistance, as will be evident from 

 the facts I have quoted from him above. Mr. Alford has also 

 kindly undertaken to see this memoir through the press for me. 

 My fiiend and pupil Mr. L. R. Crawshay has given me great help 

 in preparing the illustrations. Finally, I have to thank Monsieur 

 Topsent, of Caen, for his kindness in sending me specimens from 

 Roscoff and elsewhere and for answering many queries. 



BiBLIOGEAPHY. 



(1) BowERBANK, J. S. A Monograph of the British Spongiadse. 



London, Ray Society, 3 vols. : 1864-1874. 



(2) Haeckel, E. Die Kalkschwamme. Berlin, 1872 ; 3 vols. 



(3) Lendenfeld, R. v. Die Spongia der Adria : I. Die Kalk- 



schwamme. Zeitschr. wiss. Zool. liii. (1891) pj). 185-321, 

 361-433, pis. viii.-xv. 



(4) MiNCHiN. E. A. Sponges in : Lankester, ' A Treatise on 



Zoology,' London, 1900. 



Other references are cited in the list of synonymy, p. 17 above. 



EXPLANATION OF PLATE I. 



Clathrina contorta from Banyuls. 



A from above ; B from above, and C from the side, to show tbe oscular 

 tubes (0). 



