EUSPONGIA. 129 



are sometimes pervaded by fine membranes. The latter are particularly highly 

 developed in E. o. exigua, where they divide the peripheric part of the lacu- 

 nose oscular tubes into small compartments. The central part of the oscular 

 tube is, however, always free from these membranes, so that a clear passage is 

 left in the middle. The oscular tubes are straight and regularly cylindrical in 

 E. 0. adriatica, E. o. molKssima, and E. o. rotunda ; in the other varieties they 

 are more curved, and often very irregular. The oscula are surrounded by 

 sphincter membranes. F. E. Schulze says that the oscula are sometimes 

 covered by perforated memh7'anes. I do not believe that this occurs in this 

 species, and am of opinion that this observation may refer to his variety 

 E. 0. tubuhsa, which I do not regard as a form of Euspongia at all, but as a 

 Eippospongia . 



The skeleton consists of main and connecting-fibres. The former extend 

 radially from the base upwards and terminate in the conuli. They are gene- 

 rally only slightly ramified. The branches are given off under very sharp 

 angles, and soon attain a direction parallel to that of the stems. Only in E. o. 

 lohosa the main fibres are much and irregularly branched. The main fibres 

 are knotty or pretty smooth, and always contain foreign bodies ; these are 

 generally pi-etty scarce, scattered, and confined to the axis, more abundant 

 in E. 0. dura and in E. o. lohosa than in the other varieties. Those of 

 E. officinalis, var. spinosa, contain large spicule-fragmeuts and appear very 

 spiny. The connecting-fibres are of comparatively uniform thickness. The 

 thinner ones — not taking young fibres into account — are never less than half 

 as thick as the thickest. They are always free from foreign bodies. The main 

 fibres measure 0-04-0-2 milHm. in thickness, in most of the varieties from 0-04 

 -0-06 millim. ; some of them are as much as 0*09 millira. thick in E. o. eaigua. 

 The very areniferous main fibres of E. o. lohosa and E. o. dura are 0*l-0*2 

 millim. thick. The thickness of the connecting-fibres is given by E. E. Schulze 

 at 0*03-0-035 millim. Taking the young fibres into account, the measurements 

 are, according to my own observations, 0'013-0-033 millim. In E. o. nitens 

 a special surface-net of exceedingly slender fibres, measuring only 0-005-0-007 

 millim. in breadth, is described by O. Schmidt. The meshes of the network 

 formed by the anastomoses of the connecting-fibres are rounded, polygonal, or 

 elongate and irregular. In E. o. lohosa the meshes are sometimes rectangular. 

 The thickest connecting-fibres (some attaining a breadth of 0-09 millim.) are 

 observed in E, o. exigiia. The thickness of the connecting-fibres and the width 

 of the meshes are pretty uniform in the other varieties. The meshes measure 

 0'l-0-4 millim., on an average 0*2 millim., in width. 



The histology of this species has been carefully studied by F. E. Schulze. 



The species Euspongia officinalis was established in a somewhat similar sense 

 to that which I give it by F. E. Schulze in 1879. Sponges belonging to it 

 have been described first by Aristoteles, who distinguished three varieties of 



