438 Prof. W. J. Sollas on the 



vesicle possesses at least two sphinctrated orifices, one putting- 

 it in communication with the vesicle behind, and the other 

 with that in front — every vesicle, that is to say, except those 

 beneatli the pores ; for the pores are not provided with sphinc- 

 ters. The openings into the flagellated chambers are also 

 without sphincters. While two is thus usually the least 

 number of sphincters apparent in a vesicle, a greater number 

 is not uncommon, since, when a lateral series proceeds from 

 a main line, equivalent to the branching of a canal, the first 

 vesicle of the secondary series communicates with that from 

 wliich it proceeds by a sphinctrate aperture ; and thus, as one 

 vesicle of a larger series may bud off, as it were, more than 

 one subsidiary series, it may exhibit four or more sphincters 

 in its walls — two about the communications with vesicles 

 of its own order, and two or more about the communications 

 with vesicles of a lower order. The subsidiary series of 

 vesicles bud off others, and these again others, till the ultimate 

 vesicles are reached which communicate with the flagelhited 

 chambers. In this way the size of the vesicles diminishes 

 from 0*015 inch in diameter, which is the average of those in 

 the main series, down to and 0"005 to O'OOl, which is that of 

 the ultimate smallest vesicles. 



The flagellated chambers (PI. XVII. fig. 15) are spherical 

 or ellipsoidal sacs communicating by a large circular pore, 

 0'0032 to 0'006 inch in diameter, with the ultimate incurrent 

 vesicles, and by a wide mouth, from 0'00G4 to 0'009G inch 

 across, with the ultimate excurrent canaliculi. In size they 

 average 0"001 inch in diameter, and thus agree with the 

 similar chambers of the Geodina generally, and of Tetilla and 

 such Esi^eruB as I have examined. This uniformity in size 

 is in striking contrast with the differences which distinguish 

 the chambers of the Chondrosia3 and the Cerospongiai ex- 

 amined by ScliLilze, and leads one to suggest that it may 

 result from close genetic relationship. 



The excurrent canaliculi lead directly into the nearest 

 vesicle of the excurrent system, about Avliich the flagellated 

 chambers are clustered in a concentric layer (PI. XVII. fig. G,/"). 

 Excepting the canalicular form of its ultimate branches, 

 the excurrent exhibits the same vesicular cliaracter as the in- 

 current system. 



The oscule is a more or less circular opening, averaging 

 0*1 inch in diameter, usually situated in the midst of a gently 

 rising conical eminence; its circular margin is thickened into 

 a lip or annulus of a bluish translucent cartilaginous ap])ear- 

 ance ; and immediately outside this is a surrounding fringe of 

 long acerate spicules. The oscule leads into a wide excurrent 



