PROTOZOA I SPONGIDA. 7 I 



less number of inhalant " pores." There are, in fact, many 

 who hold that the more complex sponges are merely pro- 

 duced by the aggregation together of a number of these simpler 

 colonies. 



The "sarcoid" has been shown by Mr Carter to be "a 

 granuliferous polymorphic body, possessing a nucleus and one 

 or more contracting vesicles." It has also been shown that 

 the monociliated sarcoids possess, in some cases at any rate, 

 a membranous cylindrical collar round the base of the cilium, 

 similar to that which has been observed in the Flagellate In- 

 fusoria. To construct a typical sponge, therefore, we must 

 imagine that a number of sarcoids, such as above described, 

 are aggregated to form a community of a somewhat spherical 

 shape, with a common circular aperture ; that each sarcoid 

 has the power of taking food into its interior, and of discharging 

 the indigestible portions, after the manner of an Amoeba; and 

 that the circular aperture opens and closes itself as required by 

 the needs of the colony. We have further to imagine that 

 these spherical communities are the essential elements of the 

 sponge, and that they are embedded in countless numbers in 

 the sarcode of each individual sponge, constituting the so-called 

 " ciliated chambers." 



In a living sponge a constant circulation of water is main- 

 tained by means of an aquiferous system (fig. 12), which is 



Fig. 12. Diagiammatic section o(Sfrngilta (after Huxley), a a Superficial layer or 

 "dermal membrane ; " b b Inhalant apertures or " pores ; c c Ciliated chambers ; 

 d An exhalant aperture or "osculum." The arrows indicate the direction ot 

 currents. 



constituted by the oscula and pores already alluded to and 

 by a system of canals excavated in the substance of the 

 sponge, and uniting the two sets of apertures. The water 

 passes in by the " pores " or inhalant apertures, and is con- 

 veyed by a series of canals the "incurrent" or " afferent''' 



