Mr. li. J. Carter on the Uttiinate Structure of Spongilla. 27 



T have stated that the contents of the ovi-bearing cell during 

 development become spread over its inner surface, but at the 

 same time I think it questionable whether this cell becomes 

 revivified, or whether it is not ultimately cast off after a new 

 one has been formed. 



In proportion as the ampullaccous sac experiences a want of 

 nourishment after it has beeu fully developed in the watch-glass, 

 so it gets thin, and, becoming more translucent, not only allows 

 its aperture to be better seen, but presents an indistinct meri- 

 dional lineation, which, radiating from around the aperture, 

 meets at the opposite pole of the sac, thus giving the former an 

 api)earance not unlike the pupil of the eye (fig. 3 a) ; but though 

 at one time it is larger and at another smaller, and not unfre- 

 quently of an irregular circular form, yet its changes are so 

 gradual, that I have seldom, except when carmine has been 

 added and taken into this sac, been able to see any alteration in 

 its size or form for an hour together. When the aperture is in 

 focus, the opposite point of the sac is invisible. 



Afferent Canals. — The afferent canals consist of a number 

 of channels which open by large apertures into the paren- 

 chyma from the cavity of the investing membrane, and then, 

 freely anastomosing, form an areolated cavernous structure, 

 throughout which the particles admitted into the cavity of 

 the investing membrane subsequently circulate, and are finally 

 received into the ampuUaceous sacs which open into them 

 (fig. 1 e, e). 



Efferent Canals. — The efferent canals, on the other hand, 

 begin by radicles in the interstices of the cavei'nous structure, 

 among the ampuUaceous sponge-cells (with the cavities of which, 

 however, they do not communicate, nor with the afferent canals, 

 as will be seen hereafter), and, growing into large branches, at 

 length terminate in a single tube. This tube extends beyond 

 the periphery of the Spongilla, and ends in a mammilliform 

 point, in the centre of which is a single contracted aperture 

 (PI. I. fig. 1^). 



Thus we have the structure and composition of the portion of 

 Spongilla developed from the seed-like bod)^ Let us now direct 

 our attention to its functions, which are easily elicited by placing 

 a little carmine in the water, and watching the particles as they 

 pass through its substance. 



No sooner has the carmine reached the exterior of the invest- 

 ing membrane, than its particles are rapidly drawn in through its 

 apertures, not vortically but directly, and, traversing its cavity, 

 or the interval which exists between the investing membrane 

 and parenchyma, in different directions, are thence drawn in 

 through the apertures of the latter, and finally into the ampul- 



