r. PORIEFERA. I. 



14 



i_-2""n, but also smaller openings are found between them, down to a diameter of 0-2'"'". The greater 

 openings are partly placed in transverse rows, however with some irregularit)-. The course of the 

 canals is chiefly very regular; below the skin the openings of the incurrent canals are found as small 

 round subdermal cavities, and the canals stretch almost directly from here, by and b\- uniting to 

 principal canals, in a curved manner obliquely inward and upward, and open into the oscular tube; 

 accordingh" all the openings in this tube are turned somewhat upward. The membrane covering the 

 oscular tube, rests on the skeleton below, which forms an irregular net of meshes, but no spicules 

 project, so that the inside of the oscular tube is not shaggy as the outer surface of the sponge. The 

 pores are found rather closely in the dermal membrane, sometimes so closel)- set, that the membrane 

 forms only thin strings between them; they have been measured to a size of 0-04 — 0-268'""'. 



The skeleton is chiefly of the common structure, onh- with the modifications necessitated by 

 the form. Immediately below the skin covering the oscular canal, an irregular network is found, 

 corresponding to the skeletal tissue found in the middle of a cylindric or leaf-shaped Chalinine. From 

 this primary fibres bending upward in a curved manner, run to the surface which they meet at a 

 right angle, and there the>- are projecting. These fibres are connected to a rather regular net of 

 meshes by spicules that form no coherent fibres, but most frequently are single; the meshes are quadratic 

 or rectangular. The rather regular net formed in this way, gets a less regular appearance on account of 

 the many canals running through it; as these grow in width inwardly, the net apjjears to be closer 

 towards the surface and more open inwardly, but this appearance is only owing to the lacuna; made 

 by the canals, while the skeletal net itself is of the same width. This skeleton is almost exclusively 

 unispicular, primary fibres with two or three spicules alongside being only found here and there; the 

 distance between the primary fibres is fixed by the length of the spicules and is on an average 0-2'""'. 

 Besides the skeleton described some polyspicular longitudinal fibres of different thickness are found; 

 they originate in the stalk, which is almost exclusively formed by such fibres and consequenth' is 

 very firm and hard, and they run longitudinalh through the sponge branching off and also anasto- 

 mosing. Upwardly they become thinner; they have a thickness of from 0-24""" down to o-o6"'", but at 

 their base in the stalk their thickness may be up to o-5""". They run in greatest number in the inner 

 part of the wall of the sponge towards the oscular tube, but they have otherwise no regular course. 

 The spongin is in the skeleton present only to a comparatively small degree, it is seen copioush and 

 distinctly in all the nodes, and it may often under sufficienth- magnifying povers be seen stretching- 

 down along the spicules or quite surroimding them with an exceedingly thin layer, but in many 

 places it seems to be confined to the nodes. Neither do the polyspicular longitudinal fibres show any 

 spongin-sheath, but they are nevertheless, as is seen by coloiiring, quite or almost quite surrounded 

 b}- an exceedingly thin layer of spongin. The spicules are in these fibres rather regularly arranged 

 in bunches, and where the ends of the bunches catch each other the spongin is most distinct and is 

 seen as a slighth- yellow-coloured transverse band. 



Spiciila are oxea, most frequently slightly and e\euly curved, rarel\- straight; the>- are rather 

 gradually and sharply pointed; the length varies from 0-23—0-29'""', the thickness is between 0015 and 

 0-02™". Shorter and finer spicules up to exceedingh- fine ones are found, but in rather small numbers, 

 the finest ones have a length of ca. 0-13'"'". 



