THE SPOXGIDA OR PORIFERA. 353 



regards the second plan, Lieberkiihn showed in 1856 that the 

 flagellate cells in Spongilla were limited to certain dilations, or 

 ciliated chambers^ of the canal system. In 1857 Carter also 

 found that, in an Indian species of Spongilla^ the flagellate cells 

 were only found as a single lining of small rounded cavities^ 

 which he called ampullaceous sacs, excavated in the sarcode of the 

 Sponge. James Clark, in 187 1, described similar cavities lined 

 with flagellate cells, under the title of monad chajuhers, in the 

 American Spongilla. " A similar ampullaceous disposition of the 

 collar-bearing cells," observes Saville Kent, " is found to obtain 

 among a very extensive series, if not throughout the majority of 

 the Spongida; in fact, all the known members of the Myxospongia 

 (gelatinous sponges), the greater part of the Siliceospongia (silice- 

 ous sponges), and in accordance with the representations given by 

 Professor Haeckel, the family of the Leuconidce among the 

 Calcispongia (calcareous sponges)." The accompanying diagram 

 (Fig. I, Plate XVI.) represents a vertical section of Halisarca^ 

 the jelly sponge; and here we see spheroidal ciliated or mo7tad 

 chambers, or ampullaceous sacs (b, b), the afferent canals leading 

 into them from the pores (a, a), and the eflerejit canals (c) passing 

 from them to an osculum. Saville Kent, in Vol. III. of his 

 "■ Manual of Infusoria," gives an illustration of " Esperia, a 

 siliceous-spiculed sponge, in vertical section, showing grape-like 

 arrangement of the ampullaceous sacs round a single afferent 

 or pore system." 



There can be no doubt, from the facts related, of the essential 

 importance of the flagellate collared cells in Sponge structure, 

 whether considered as the endoderm, or lining, of digestive cavities 

 or simply as Infusoria associated together in compound colonies. 

 Those who advocate the latter view, and especially Saville Kent, 

 lay great stress on the exact resemblance or identity of the 

 collared cells of the Spongida with the independent collared 

 animalcules {Choano-flagellata). Here is a diagram (Fig. 5, 

 Plate XVI.) representing an independent collared monad — Mono- 

 siga gracilis — as described by Saville Kent. This animalcule 

 is found attached by a slender stalk to zoophytes and sea-weeds ; 

 and it is possessed of a flagellum {b\ collar {a), neucleus {d) with 

 neucleolus, and contractile vesicles {e, e), all of which are found, 



International Journal of Microscopy and Natural Science. 



Third Series. Vol. IH. z 



