round the Cilium of the Sponge-ceU. 7 



in clusters on branches of the delicate little seaweed called 

 Calliihamnion roseum^ which fringes the overhanging edges 

 and under surfaces of the rocks here, about midway between 

 high- and low-water mark, where it. is left uncovered by the 

 water for some houi's twice a day. 



Thinking, therefore, from its hardiness, that it might serve 

 to confirm Prof. James-Clark's observations on Leucosolenia 

 hotryoides {I. c), I, about six weeks since, brought home some 

 branches of the GalUtJiamnion bearing specimens of Qrantia 

 compressa, which were put into salt water on the spot ; and 

 the day after, as these sponges were still living, I tore up 

 some pieces and placed them under the microscope, with \-oi- 

 an-inch compound power for observation, when, much to my 

 gratification, I witnessed exactly what Prof. James-Clark had 

 described, as may be seen by reference to the four groups of 

 figures (13-16 in PI. I.) which were then made from them. 

 I also saw immediately that the "ear-like points or spines" 

 on the monociliated sponge-cell of Spongilla^ which may be 

 found fully described and figured in the ' Annals ' (Jan. 1859, 

 vol. iii. p. 14 &c., pi. 1. figs. 12, 13, 14) were, as Prof. 

 James-Clark had suspected (footnote, p. 21, loc. cit.)^ " the 

 right and left profiles of a membranous cylindrical collar." 



Feeling satisfied that Prof. James-Clark was right in his 

 interpretation of this form of sponge-cell, and having, by ex- 

 periments on Spongilla^ as may be seen in my figures [1. c), 

 showed that, when immersed in a solution of indigo, the 

 sponge-cells with " ear-like points " became more or less filled 

 with it, I, of course, thought that the sponge-cells of Grantia 

 compressa might do the same, when it would become satisfac- 

 torily evident that the same kind of ciliated sponge-cell existed 

 in both the siliceous and calcareous sponges. 



Accordingly, about a fortnight since, I took a branch of 

 Callithamnion roseum on which there was a cluster of Grantia 

 compressa, and, having placed it, as before, in sea-water on the 

 spot, brought it home, rubbed down a little indigo, also in 

 sea-water, and put the cluster into it. 



After about an hour, all the specimens of Grantia compressa 

 became of a dark-blue colour ; and on cutting out a minute 

 portion of one and tearing it to pieces, still in sea-water, the 

 fragments were thus placed under the microscope, on a glass 

 slide under a glass cover, when, equally to my gratification, I 

 found the collared monociliated cells more or less filled with 

 indigo, and in active vitality (PI. II. fig. 30). 



Next the cluster was placed in clean sea-water, and a stream 

 of indigo was observed to be gradually flowing from the vent 

 of each specimen respectively. 



