STRUCTURE AND ECONOMY OF TETHEA. 415 



of the six-radiate spicula, wliile the pores in their semi- 

 octagonal recesses still remain entire ; so that these fissures, 

 and perforated grooves which result from them, may be con- 

 sidered as a linear arrangement of the spaces in which it 

 may be inferred the oscnAa ought to develop. As an addi- 

 tional evidence in favour of the opinion I have already 

 stated in reference to the position which the oscula of Tethea 

 ought to occupy, I may refer to Mr. Huxley's recent account 

 of an Australian species, in which he found irregular aper- 

 tures or prominent tubercles on the surface. Now these 

 could not have been pores, which he does not appear to have 

 looked for. They must have been oscula ; and their relations, 

 as far as they are given, are in accordance with this sup- 

 position. 



I have arrived at the conclusion, therefore, that there are 

 afferent orifices or pores in T. cranium, and in the Tethea 

 now under consideration, but efferent orifices or oscula exist 

 in neither. How the water and animal debris escape from 

 T. cranium I have not yet determined ; but if I may hazard 

 an opinion as to their mode of exit, it is that they pass off 

 through the older and more open portions of the rind, where 

 the central or radiating spicula are nearly laid bare, or have 

 begun to project. Although the rind is continuous in T. 

 cranium, it is never, as far as I am aware, uniform : the 

 more recent portions are smooth, without projecting spicula 

 or conical elevations ; the portions of medium age present 

 the characteristic conical projections ; the more ancient 

 portions are comparatively open and porous, the projections 

 have disappeared, and the radiating spicula project. These 

 more ancient portions of the rind of T. cranium correspond to 

 the rindless portions of the surface of the Spitzbergen species. 

 From these facts and considerations I have come to the 

 conclusion, provisionally — 1st, That neither T. cranium nor 

 the Spitzbergen T. possesses efferent orifices properly so called ; 



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