FOURTH REPORT OF THE DIRECTOR I907 



161 



former was internal. These are silicious sponges allied to Euplec- 

 tella and though we find no parallel expression of commensalism 

 in the living glass sponges, yet Euplectella carries a parasite in the 

 form of a crustacean which in youth enters its open cloacal cavity 

 and remains there so that when the sponge has in adult growth 

 built the terminal or sieveplate over its aperture the crustacean is 

 wholly and permanently caged. 



A very commanding illustration of the association between the 

 sponges and spiral annehds is afforded by a series of specimens 

 displayed in the British Museum. These I am able to re- 

 produce here by the kindness of the trustees of that Museum from 

 photographs made by permission of the Keeper of the Depart- 

 ment of Geology, through the friendly agency of Dr F. A. Bather. In 

 all these specimens it would appear that the worm, which has made 

 a tube of large dimensions, began its commensal existence early in 

 the Hfe of the sponge and has coiled upward in a A'ery loose spiral 

 about and just within the cloacal wall. Of the figures given here two 



These and the figure on the preceding page represent silicified sponRes with spiral anneliil 

 tubes from the English Chalk. In the u[)per figure (locality unknown) and the lower right- 

 hand figure ( Beckhampton ), the exposed worm tube is coiled about a vertical tube which 

 appears to be the silicified wall of the cloaca. These spirals are obviously in reversed direc- 

 tion. The lower left-hand ffgure is a direct print from a thin section of another sponge in 

 which the position of the worm tube, cloaca and concentric structure of the sponge are 

 shown. Prepared by Dr. Bather. Figures about natural size. British Museum (Natural 

 History) Department of Geology: A. 475; 55117 



