220 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



may expect tliat in large specimens these fibres would be 

 branched, as is the case in other species of Aplysilla. 



A vertical section through the sponge shows a well- 

 defined dermal membrane, 0*024 mm. thick ; large but flat 

 subdermal cavities (0 - 25 mm. broad, O028 mm. deep). 

 The floor of the subdermal cavities is frequently seen to 

 be perforated and to open by a narrow passage into large 

 cavities, the inhalent canals (this is not figured on PI. 

 XII). The subdermal cavities, therefore, seem to be dis- 

 tinct from the inhalent canals. The flagellated chambers 

 are large and sac-like, somewhat irregularly oval (in cross 

 sections, of course, more or less round), and may be simple 

 or bilobed (see PI. XII, fig. 1.) Their average size is 

 - 08 by 0"04 mm ; but the large flagellated chamber on 

 PL XII, fig. 1 measures 024 by 0"06 mm. They open 

 directly with a wide mouth into the large exhalent canals. 

 The chamber system is therefore eurypylous. The lining 

 of the flagellated chambers consists of cells in the shape 

 of truncated cones. In a few cases I could see something 

 like highly transparent pointed projections in front of these 

 cells. They might have been " Kunstprodukte," or 

 amoeboid processes, or, in fact, anything, but certainly 

 they did not show the slightest resemblance to those 

 notorious structures, the collars and flagella, which are so 

 often met with in literature, and so rarely in reality. The 

 endodermal lining of inhalent and exhalent canals is 

 distinctly squamous epithelium. 



The ground-substance of the mesoderm is probably hya- 

 line. It is full of fibrous tissue, and contains numerous 

 stellate (amoeboid) cells and large gland cells. The 

 stellate cells are met with in all parts of the meso- 

 derm, but they are found most crowded along the spongin- 

 fibres. They become elongated and finally thread-like, 

 where the fibres project beyond the level of the sponge. 



