122 On the Mode of Circulation in the Spongida. 



fig. 9), and underneath this a layer of ?-muscular fibrillee 

 partly longitudinal and partly transverse (fig. 6) . 



Thus, assuming that the cells had been monociliated they 

 must have had some office ; while assuming that the fibrillous 

 layer was muscular (and I do not see what else it could have 

 been), this would have the effect of circular and longitudinal 

 motion respectively. Hence, supposing that the circular 

 folds, more or less extending round the surface, were influ- 

 enced by this motion, it would have the same effect upon the 

 contents of the excretory canal as that of the intestine upon its 

 contents, which would be to propel them onwards to the vent 

 (or the reverse, if necessary) , and thus resemble the " val- 

 vulie conniventes " of the latter. Of course, the transverse and 

 longitudinal fibrillar of the excretory canal can no more be ex- 

 pected to be identified by the so-called "striped" appear- 

 ance than the muscular fibres of the intestines. 



Still, it might be observed that, although this can be de- 

 monstrated in Axos spinipoculuiti) it may not be the case in 

 other sponges ; but if we are to deny the existence of rao- 

 tory structure in moving objects because it cannot be demon- 

 strated by the highest microscopic powers, we might as well 

 deny that there is any structure in glass because it is trans- 

 parent ! 



EXPLANATION OF PLATE IV. 



Fig. 5. Ilalichondria scabida, diagram showing the direct connection of 

 the pore-areas with the excretory canal, a, pore-areas ; b, sub- 

 dernial cavities ; c, excretory canal ; d, circular folds, more or 

 less extending round the surface of the excretory canal ; e, .aper- 

 tures of branches in this canal ; /, filament introduced to show 

 the direct communication of the pure-areas with the excretory 

 canal ; ff, vent. 



Fig. 7. Teichonella labyrinthka. Perpendicular section of a chamber, 

 with all its parts drawn to scale, viz. about l-48th to 1-I800th 

 inch, the arrows indicating the direction of the circulation. 

 a a, Chamber ; b, pore-dermis, leadiug into c, subdermal cavity, 

 and the latter leading into " a «," the chamber ; d, subdermal 

 tissue; e, surface view of pore-dermis ; /, opening of subdermal 

 cavity, as seen through the pore-dermis; ff, pores in the wall of 

 the chamber ; h, spongozoa in the same ; i, vestibule of the 

 vent ; k, sphincter of the vent and opening through the same, 

 shown by the arrow ; I, interoscular tissue ; m, end view of 

 sphincter, surrounded by interoscular tissue, and arrow showing 

 the direction of the current ; n, diagram, to show horizontal 

 section of the chambers in their natural position, with the in- 

 tervals between them ; o, chambers ; p, intervals or intercameral 

 tissue in which the ova are developed, and in which the branches 

 of Hackers " intercanal system " are situated. 



