STUDIES ON THE COMPAEATIVE ANATOMY OF SPONGES. 19 



radially from the chambers into the surrounding matrix." 

 " The whole appearance is suggestive of a contraction of the 

 choanocytal wall under the influence of some strong stimulus, 

 possibly of the alcohol into which the ^sponge was plunged on 

 removal from the dredge." 



Doubtless the unusual appearances of the chambers observed 

 by Sollas and myself are in both cases due to contraction; and 

 had I seen only such cases as that represented in fig. 29, x, I 

 should have been strongly inclined to regard the contraction 

 either as a merely temporary condition or as a post-mortem 

 condition, produced, as suggested by Sollas, by the action of 

 the alcohol. The appearances presented in fig. 28, however, 

 in which the gelatinous matrix around the chamber has regained 

 its normal condition, while the chamber is more contracted 

 than ever, seem to me to demand a difl'erent explanation, 

 which I have endeavoured to give above. 



The Exhalant Canals, 



Since the flagellated chambers do not extend to the actual 

 gastral surface, but are separated therefrom by the entire 

 thickness of the gastral cortex (fig. 26), the existence of special 

 exhalant canals becomes necessary in order to place the 

 chambers in communication with the gastral cavity. These 

 exhalant canals are short, wide, cylindrical tubes, sharply 

 marked off" by the sphincter diaphragms already described 

 from the chambers at the one end, and opening directly, with- 

 out any narrowing or diaphragm, into the gastral cavity at the 

 other (fig. 26). 



I have already had occasion to mention that sometimes an 

 unusually small exhalant canal is met with, cut transversely, 

 in tangential sections of the cup wall a little below the level of 

 the ordinary exhalant canals. Such small canals are surrounded 

 by quadriradiate spicules of a slightly unusual form (fig. 21). 

 I am at a loss to explain the existence of these smaller canals, 

 with their slightly peculiar spicules, unless they be simply 

 the exhalant canals of young interpolated flagellated chambers, 

 surrounded by young spicules. This view is supported by the 



