G42 ON THE FIBRES OF CERTAIN AUSTRALIAN UIRCINID^i. 



other foreign body would have. In Sponges as in higher animals 

 foreign bodies are always encrusted by the substance the skeleton 

 is made of. Particles of sand which enter the Sponge are covered 

 by a thin layer of horny substance. 



They are consequently soon covered by a thin layer of horny 

 substance, which may suffice to kill them. Their substance is 

 absorbed by the Sponge, and the vacant space filled with horn- 

 substance. In this way a structure could be arrived at, which is 

 similar to an Oscillaria as far as the shape, and similar to the 

 horn-fibres as far as the chemical structure, is concerned. 



A series of these Hirsinidse possesses a horn fibre skeleton, which 

 is very different from the skeleton of the known Hircinidte, but 

 differs also from any known form of horny fibre. 



Numerous minute horny fibres running in various directions and 

 continually anastomosing form a column of reticulate horny-sub- 

 stance which corresponds to an ordinary main fibre. It is hardly 

 thicker than the homologous fibres in other Ceraosponges. A great 

 number of Hircinidaa possess this character. 



Fleming described (WUrzburger physikalisch-med. Verhandl. 

 II., Seite 1) extraordinary cells in the fibres of Janthella. I have 

 had occasion to study similar highly pigmented cells in some 

 hornsponges which possess filaments. These pigment cells are 

 large and distributed in pretty regular cylindrical layers between 

 the layers of horny substance in the fibres. These cells cause the 

 deep black colour of the fibres, but certainly have nothing what- 

 ever to do with the growth of the horny fibres as Carter assumes. 

 (On the development of the fibre of the Spongida Ann., Mag. (.3) 

 VII., p. 112). 



These cells might possibly also turn out to be small algae, which 

 like the yellow cells in other animals live symbiotic with the 

 Sponge. 



Their constant occurrence in certain species cannot influence 

 the hypothesis, as the yellow cells in higher Coelenterata are also 

 always found in the same species. 



