of Foreign Bodies by Sponges. -^97 



Dendoriclne species Tedania commivia, R. & D., and in tlie 

 Ectyonine j^enus Aulena. In Psammopemma anion;^ Ceratoaa 

 and in Tedania comntixta the foreign bodies are not enclosed 

 in fibres, but lie in the ground-substance. Professor Minchin * 

 speaks of this phenomenon as a " remarkable property- 

 possessed })y the spongin fibres," and says, " Sand-grains . . . 

 and such-like bodies which fall on to the surface of the sponge- 

 body become included in the fibres, apparently by adhering 

 to the tip of the fibre at its growing point, where it is con- 

 tinuous in all probability with the external cuticle of the 

 sponge-body, Tiie absorption of foreign particles into the 

 spongin fibre is therefore not so mucli a question of their 

 travelling down into it as of their being passively surrounded 

 by spongin as the fibre grows upwards." 



The appearaTice of the surface of the present species 

 suggests that here, at any rate, inclusion takes place in a 

 different manner. In thick freeliand sections the sand-grains 

 lying on the surface are seen to be enveloped by the super- 

 ficial tissue of the s))onge, which is raised up round them and 

 adheres to them. Sometimes pseudopodia-like extensions of 

 the sponge-tissue are found partially enwrapping the grain 

 (fig. 1). When sand-grains are found, as in fig. 2, attached 

 to the apex of a conulus, I believe that this results from a 

 flow of material to the neighbourhood of the irritant grain, 

 not from the sand-grain having fallen upon the summit of a 

 conulus. 



The abundance of sand-contents makes it difficult to cut thin 

 sections while the grains are in place, the tissues were therefore 

 demineralized with hydrofluoric acid. In sections of material 

 treated for a day or two with this reagent some remnants of 

 siliceous fragments were still present, but the outer layers 

 were sufficiently free to admit of fairly thin sections being 

 cut. In these sections it is seen that in the cortex there are 

 numerous cells containing coloured granules; of these some 

 are confined to the cortex, others aggregated in oval cell- 

 clusters occur throughout the tissues. In both cases the 

 granules conceal the nucleus. The granular cells are fre- 

 quently elongated and fusiform ; sometimes, particularly 

 beneath remnants of foreign bodies (fig. 3) and on the flat 

 summits of the low ridges of the cortex, they are of irregular 

 rounded shape or lobed, and they are massed together in 

 numbers. The surface of the sponge appears to me to be 

 absolutely devoid of cuticle and to be bounded by granular 

 cells. This observation was found to hold good also in 



* ' A Treatise on Zoology ' (edited by E. Ray Lankester), 1900, p. 42, 



