194 THE CANADIAN NATURALIST. [June 



Were the tubes of Receptaculites to be closely crowded together 

 so that their walls would everywhere be in contact, and no space 

 between them, then the structure would be similar to that of 

 Orhitolites, but with the system of connecting stolons arranged on 

 a different plan. The genus would then also closely resemble 

 Dactylopora ; but I do not yet see that the evidence is sufficient to 

 prove clearly that the tubes are strictly the homologues of the 

 cells of any group of the Foraminifera. They appear to me to be 

 more nearly related to the connecting spicula of the SpongidsD. 

 Each tube with its cylindrical shaft, and plate at each extremity, 

 resembles not remotely a birotulate spiculum. Or it might perhaps 

 with more probability be described as consisting of two spicula 

 united at their points. Thus the ectorhinal plate with the four 

 stolons may be a peculiar form of the foliato-peltate spicula, of 

 which many different kinds are figured by Bowerbank. The 

 cylindrical shaft may be a spiculum approaching the acuate or 

 acerate varieties with its point inserted into the nucleus of the 

 foliato-peltate spiculum. Most sponge spicula are hollow ; and we 

 know how often it happens in the structure of the animal kingdom 

 that organs may at one time subserve one function, and elsewhere 

 a very different function. The cylindrical cavity, which in the 

 spicula of the ordinary sponges seems to be functionless, may in 

 Receptaculites be transformed into a canal for the transmission of 

 fluids. But although the cavities of all the tubes in Recepta- 

 culites communicate with each other through the endorhinal canals, 

 and perhaps through the stolons also, they may not constitute a 

 canal-syste'm. The so-called tubes are extremely slender, and may 

 be solid in some species. 



On comparison it will be found that the general form of Recep- 

 taculites and structure of its body-wall is almost precisely that of 

 the seed-like body that plays so important a part in the devel- 

 opment of Spongilla. This consists of a small ovate or spherical 

 sac with an aperture on one side leading into the cavity within. 

 The enclosing wall consists of a coriaceous membrane on the out- 

 side of which there are arranged, perpendicularly to the surface^ 

 numerous small birotulate spicula, exactly as the tubes of Recepta- 

 culites are arranged on the endorhin. The outer extremities of 

 these spicula give off at right angles a number of small spines 

 corresponding to the stolons above figured. These spines coalesce, 

 and (if I understand the figures rightly) become connected 

 together, so that they form by their union a plate similar to that of 



