122 



t. I.II MA. 



I bave mentioned is a normal and constant fact whenever the natural 

 apical end is found preserved. But it may here be mentioned in antici- 

 pation that neither the presence of the branches nor of the oscula on 

 the stem seems to stand on the way of the above speculation. For, the 

 former are known to occur sometimes even on the basal disc for attach- 

 ment, and the latter too seem to be something, which, as a general 

 matter in the Euplectellida*, may occur almost in any part of the sponge 

 body. In P/acosoma paradictyum, a new stalked Euplectellid which 

 will soon be described elsewhere, oscula aie present on the stalk as well 

 as on the basal disc in addition (o those on the body proper. 



Be that as it may, a stalk is always but a part of the sponge-body r 

 and there stands nothing against, the indictment that Walteria leuckarti 

 is a tubularly developed fumi, with a small terminal osculum at the 

 superior end and a 7iuinber of larger oscula on the sides. 



The terminal osculum is in all probability the first formed in an 

 early stage of the post-larval development ; it should be strictly homolo- 

 gous with the similarly situated simple osculum of other Hexactinellids 

 (Malacosaccus, Saccocalyx, the young of Begadrella okinoseana, — to 

 take examples from amongst the Euplectellids). On the <.ther hand, 1 

 hold the oscula on the sidi's of Walteria leuckarti as morphologically 

 equivalent to th >s ; openings in certain Euplectellids (Euplectella, 

 Megadrella, &c.\ which were called '' parietal gaps " by F. E. Schulze 

 and " parietal oscula " by me. Xow, whereas it is a general rule with 

 the Euplectellids that the final outflow of water from the body is effected 

 principally, if not entirely, at the superior end either by a simple large 

 osculimi or a congregation of separate orifices (sieve-plate meshes 

 simulating it to the best under the architectural circumstances, and the 

 parieLal oscula, if present, apparently play only a subordinate ròle in the 

 discharge of that function, — we seam to have in Walteria leuckarti a 

 peculiar exceptional case in which the matter is reversed. Here, 

 nam dy, the terminal osculum is abortive while those on the sides are so 

 much the more developed as to be indubitably recognizable as such. 



