BY R. VON LENDENFELD, PH.D. 493 



canals with a circulai- or oval transverse section and an average 

 widtb. of 3 mm. These join to form a pseudogaster which opens 

 by a slightly raised pseudosculum in some specimens. In others 

 no ti'ue pseudosculum has been observed, but generally such are 

 well defined. They are from three to ten in number. We will 

 find them much higlier developed and most remarkaVjle in 

 Eitsjjongia canaliculata. Easpongia irregularis lutea possesses no 

 vestibule space. 



In Euspongia irregularis tenuis on the other hand it is very 

 highly developed, and formed of similar anastomosing canals as in 

 the variety silicata. No pseudoscula have been observed in the 

 specimens of this variety, as the vestibule canals open irregularly 

 and indiscriminately over the whole surface. 



Eusjjongia irregularis Jacksonia is similar, as far as the develope- 

 ment of the vestibule spaces is concerned, to the variety tenuis. 



B. True Canals. 



The canal system of all the varieties is the same. In fact if I 

 found two similar sponges with any difference in their canal 

 system I would consider them as two distinct species. 



In each pore-sieve there are one or two large inhalent circular 

 or oval pores measuring on an average 0-03 mm. in diameter. Of 

 course their size greatly depends on circumstances. I have never 

 observed them to be entirely closed, but I believe that the strong 

 muscular cells which are disposed in rings around them, so as to 

 form true sphincters, can contract them to a quarter of their width 

 when dilated. The largest I have seen measured 0'05 mm., the 

 smallest 0'012 mm. across. 



From these pores narrow canals lead down in an oblique direc- 

 tion through the thick skin. These canals average a width of 0-04 

 mm., which measurement corresponds with the measurement of the 

 dilated pores as seen from the surface very well. The skin is on 

 an average 0'06 mm. thick and below it the sub-dermal cavities 

 extend. These cavities are formed by tangentally extended canals 

 of a circular transverse section, which form frequent anastomoses 

 and undermine the skin throuarhout the entire surface. 



