Spongia coriacea (t/* J/on^a(7M. 19 



This network is composed of a hollow anastomosing thread 

 or tibre of variable diameter, whose interstices or meshes (for 

 a parallel illustration of this meshwork see the body of 

 Leucosolenia lacu7iosa, var. Hillieri^ PI. I. fig. 2, a, f^ g) are 

 subject to infinite variety both in size and shape throughout 

 the specimen, which, when large, thins out from a massive 

 variable amount of thickness in the centre, seldom more than 

 2 or ij-12ths of an inch, to a single reticulated layer at the 

 circumference. These thickened centres are numerous in a 

 specimen about the size mentioned, and form several little 

 monticular elevations scattered over the surface, whose sum- 

 mits respectively end in a little short open tube with naked 

 margin, which is continuous with the neighbouring branches 

 of the hollow thread-work, and thus forms an osculum 

 or vent to this part of the sponge (see also PI. I. fig. 3), 

 while the other ends of the thread are blind and attached to 

 the rock over which the sponge may be growing. So that 

 the hollow of the reticulated thread is homologous with the 

 cloacal cavity of the other forms of Calcisponges. 



If we follow the development of this structure from the 

 youngest form that can be seen, viz. that which has just come 

 from the embryo, it will be found to consist of a simple erect 

 sac, whose upper end is open and whose lower one is attached 

 to the rock on which it may be growing. This is the com- 

 mencement of the hollow thread out of which the largest 

 specimen is finally constructed. It may now be about l-30th 

 inch long by l-120th inch broad, narrowing to a point at the 

 fixed end. Such are the measurements of the smallest forms 

 which are just now (April 10th) to be seen of all sizes and all 

 stages of development on the rocks at " Straight Point " 

 here, where the species grows abundantly. In the next stage 

 the sac sends out a tubular bud, which may also descend to 

 the rock, and then, as the individual grows upwards and out- 

 wards, other similar buds are put torth which either descend 

 to the rocks for fixation or otherw ise anastomose with each 

 other, until at last the reticulated structure first described is 

 attained j but how the anastomosis is effected, that is, how the 

 loops are formed, I have not been able to perceive. 



Thus the development is very simple, although the adult 

 form appears to be so complicated, and the reticulated struc- 

 ture not by any means confined to Grantia clathrus alone, but 

 common to a great many different species of Calcisponges, of 

 which the beautiful little Leucosolenia lacunosa, Bk., of the 

 British shores is a stipitate form and also of different spicula- 

 tion ; still, whatever the spiculation may be, the soft parts 



2* 



