438 Gr. C. J. Vosmaer 



in Order to form under the dermis a kiud of large reservoir in which 

 here and there columns of Sponge-substance connect the floor mth the 

 roof of the cavity. From these subdermal cavities goes off a system of 

 canals or laeunae that penetrates the Sponge nearly reaching the inner 

 wall of each cloacal tube. These very wide canals give off numerous 

 ramifications in all directions ; the secundary branches ramify agaiu and 

 so on, but each secondary branch has a smaller diameter than the pri- 

 mary ones. Besides these wide canals the subdermal cavities give off 

 narrow ones (fig. 20 a, ß); these seem not to ramify; they do not 

 penetrate the Sponge to a great depth. In fig. 20 the difference be- 

 tween the wide and narrow canals is very conspicuous ; the character as 

 subdermal cavities with their narrow canals is very clearly shown in a 

 and ß; in y on the contrary one can hardly speak of a subdermal ca- 

 vity. A large series of sections teaches us the fact that both are ouly 

 varieties of the same principle and not at all two different cases. In 

 figs. 16, 17 and 18 I have chosen examples of such a series: in 

 fig. 16 there are for instance, two subdermal cavities marked with + and 

 ; a few sections farther in one direction we see the cavity enlarged, 

 but in stead of the cavity + we see two very small ones, and the broad 

 canal -jf deeper (fig. 18i . A few sections in the other direction show us 

 where both cavities + and are in direct communication with the canal 

 -if, that penetrates nearly the whole Sponge (fig. 17). These inhalaut 

 canals ramify during their courseinto the Sponge, the branches becoming 

 always narrower (fig. 4). Much wider are the exhalant canals. Under 

 the inner wall of each cloacal tube are immense laeunae, ramifying in 

 different directions as they go to the peripheral part of the tube, and 

 diminishing in their diameter (fig. 4). The inhalant canals begin thus 

 as wide passages, ramify and become narrower, the exhalant on the 

 contrary uniting with one another become thus wider and wider. The 

 sections of the first show as a rule a diameter greater than, or at least 

 equal to, those of the exhalant canals, in the outer parts of the Sponge- 

 tube (fig. 4). The contrary takes place in the inner parts. Of course 

 in the middle their diameter will be about equal. The two Systems of 

 canals communicate by means of the ciliated Chambers. These are 

 rather large and pouch-shaped, resembling those described and figured 

 by F. E. Schulze of S^joti^elia K They do not occur in every part of the 

 Sponge, but form a special region. Outward this region is the system 

 of subdermal cavities ; inward another system of cavities, belonging to 



1 F. E. Schulze, Zeitschr. f. wiss. Zool. XXXII. Bd. (187S). p. 153. 



