BY R. VON LENDENFELD, PH.D. i 



will show, some chambers are in direct communication with the sub- 

 dermal cavity, whilst otliers draw their supply of water from the 

 inhalent canals. These ciliated chambers are not constricted at 

 their exhalent aperture, which is circular and opens generally into 

 a narrow exhalent canal (e. fig. 3), a few ciliated chambers open 

 direct into the gastral cavity in the centre of the Sponge. 



The exhalent canal system consists of more or less radial narrow 

 canals, pointing slightly upwards towards the Osculum, these 

 canals are cylindrical and curved in such a manner, that their 

 distal portion runs for a short distance parallel to the outer 

 surface, whilst their proximal part is radial, and often stands at 

 nearly right angle with the former ; and of an extensive gastral 

 cavity taking u]i the central portion of the Sponge and traversed 

 by a few thick and ramified threads of tissue. 



The narrow exhalent branch canals have a diameter measuring 

 from 0-1 — 0*3 mm. The central gastral cavity has a diameter 

 equal to a fourth to a third of the diameter of the part of the 

 Sponge in which it is situated. The threads pervading it in 

 varying direction are distant and rare. They are more or less 

 cylindrical, and measure 04 mm. in thickness. 



Towards the Osculum they get scarcer and scarcer, in the upper- 

 most 5 mm. of the Oscular tube or Gastral cavity there are none. 

 (Fig- 3.) 



Histology. 



The Skin is covered on both sides by a low flat Epithelium and 

 contains in the Gallert of its Mesoderm three kinds of cells. 

 Amoeboid wandering cells towards the lower surface in great 

 abundance forming a regular layer (d. fig. 4) ; ordinary multipolar 

 tissue cells and an external layer of Gland cells. 



In the threads perforating the subdermal cavity, which are 

 covered by the same Epithelium as the outer skin we find bipolar 

 and multipolar tissue cells and also a few amoeboid wandering cells 

 The extensive inhalent canals are clothed with a similar Epithelium. 

 The fringe cells in the chambers are of uniform kind throughout 

 and do not become lower towards the inhalent aperture as in some 



