PROTOZOA: SPONGIDA. 85 



rise to a so-called " syncytium," or layer of structureless sarcode. 

 Regarding the skeleton as something superadded, we may 

 therefore look upon a sponge^jy^ajkmdj}f ^colony, composed 



Fig. 24. A, Portion of Grantia, highly magnified, showing the triradiate spicules and 

 the sarcoids ; B, A single sarcoid of Grantia compressa, greatly enlarged, showing 

 the membranous collar (a), the flagellum (/), the contractile vesicles (c c), and the 

 nucleus () ; C, A sarcoid of Grantia compressa, with the pseudopodia protruded 

 and without the flagellum, greatly enlarged. (B and C are after Carter.) 



of an aggregation of zooids, of which some are amcebiform, 

 others are like Flagellate Infusorians, and others are specially 

 modified to form a " syncytium." The first two kinds of these 

 zooids are capable of procuring and assimilating food for them- 

 selves, and also of independent movements; and even frag- 

 ments of the "syncytium," when detached, are capable of 

 throwing out pseudopodia. This view of the true nature of a 

 sponge becomes still more readily comprehensible when we 

 consider the simplest condition in which a sponge occurs in 

 nature (as exemplified, for instance, in certain of the Calci- 

 spongice, such as Sycandra, fig. 23, B) ; the condition, namely, in 

 which the entire^ sponge consis.l^^.a^ojojay of sarcoids, secret- 

 ing a common 'skeleton, but provided with only a single "oscu- 

 lum," and a greater or less number of inhalant "pores." There 

 are, in fact, many who hold that the more complex sponges are 

 merely produced by the aggregation together of a number of 

 these simpler colonies. 



The above-mentioned constituents of the soft parts of an 

 ordinary sponge are usually disposed as follows : The simpler 

 amoebiform sarcoids make up the bulk of the colony and form 

 the greater part of the sponge- flesh. Embedded amongst these, 



