OF THE SPONGIADJE. 151 



tirst act is to liberate itself from the membranous envelope ; 

 and the contents thus hatched become moving masses of 

 free sarcode, but without the locomotive cilia that are found 

 on the so-called ova or gemnmles of the marine sponges, so 

 minutely and accurately described by Dr. Grant in his 

 papers " On the Structure and Functions of the Sponge " in 

 the 'Edinburgh New Philosophical Journal,' vol. ii, p. 129. 

 This author describes the ova or gemmules of HaUchondria 

 panicea {Hal. incrustaiis, Johnston), after having floated 

 freely about for a period by means of the cilia around its 

 larger extremity, as attaching itself to a fixed body by its 

 smaller end and then gradually settling down in the form of 

 a broad flat mass, and after losing its cilia being gradually 

 developed in the form of the parent sponge. Thus every 

 description by these close and accurate observers tend to 

 the conclusion that the multiplication of the sponge is 

 effected by the origination in the ovum, or by the agglome- 

 ration in the form of gemmules, of particles of sarcode. 

 The action of the minute masses of sarcode liberated by the 

 bursting of the envelope of the ovum, and their subsequent 

 development, is precisely that of the so-called sponge-cell 

 liberated from the mass of the sarcode lining the interstices 

 of the sponge, and of the gemmules described by Grant 

 when sessile ; each moves independently at first ; each unites 

 with its congeners into one body : and the results, both in 

 means and end, are precisely the same, but their origin is 

 different. The one is a generation of sarcode within a 

 proper membrane in the form of an egg, while the others 

 are the production of a gemmule by independent growth, 

 or by spontaneous division of the sarcodous substance of 

 the sponge. 



Both these modes of propagation occur in the same 

 species, Spongillajluviatilis, but I have never yet seen them 

 both well developed in the same individual. Where the 

 ovaria were abundant, the sarcode appeared even and con- 

 sistent in its structure, and, on the contrary, if it exhibited 

 manifest symptoms of granulating, very few or none of the 

 ovaria could be detected. This double means of propaga- 

 tion is by no means uncommon among the Zoophytes. 



