BY R. VON LENDENFELD, PH.D. 547 



Canal System. 



From the pores in the pore-sieve mentioned above, which 

 measure, when dilated, O'Ol mm. in diameter, and which are 

 circular, cylindrical canals lead down to the sub-dermal cavities. 

 (Plate XXXVIIL, fig. 2 c). There always are a great number of 

 j)ores, as many as 30 in one pore-sieve. The canals which lead 

 down from them extend tangentally and obliquely, and join to form 

 larger canals which likewise extend tangentally. ( Plate XXX VIII., 

 tig. 1). These finally open into the sub-dennal cavity, which is 

 formed by large tangental irregular canals, separated from the 

 outer surface by a very thick skin 0-15 mm. in thickness. (Plate 

 XXXVIIL, fig. 2). 



This part of the canal system is very similar to corresponding 

 parts of the canal system in certain Gumminse (1). 



The sub-dermal cavities measure 0*14 mm., on an average in 

 width, although there ai-e here and there spaces 0-6 mm., wide. 



From this net work of tangental canals which forms the sub- 

 dermal cavity, canals extend obliquely downward which x'apidly 

 ramify in an irregular manner. These branches supply the sponge. 

 Their size of course is very variable but they rarely exceed 0*2 mm., 

 in diameter and mostly have a circular transverse section. 



The ciliated chambers are attached to the final ramifications of 

 these canals without the formation of any special canals leading to 

 the chamber pores as in Uuspongia officinalis. The chamber pores 

 are also much smaller and apparently more numerous. 



The small exhalents join to form large canals which are irregular 

 and may attain a width of 0' 7-0 -9 mm. These join and form the 

 oscular tubes which are generally vertical to the surface and 

 straight, with a circular transverse section. They are about 

 1*2 mm. wide, and extend nearly right through the lamellose 

 sponge. Into the sides and particularly into the lower portion of 

 this oscular tube, these exhalent canals open. 



(1) F. E. Schulze. Untersiichungen iiber den Ban und die Entwicklung 

 der Spongien. Dritte Mittheiluug. Die Familie dor Chondrosidas. Zeitschrift 

 fiir wissenschaftliche Zoologie. Band XXIX., Seite 87. 



