I 66 NATURE AND AFFINITIES OF THE SPONGES. 



given of it, but it practically represents the most actively motile and 

 important element in the animalcule's economy. During life, in its typical 

 fully-extended state, a continuous stream of fine granular protoplasm 

 is ever flowing up the exterior and down the interior surface of the 

 collar, in all ways identical with the protoplasmic circulation or cyclosis 

 exhibited in the extended pseudopodia of the Foraminifera and other Rhizo- 

 poda. In other words, this structure with its circulatory currents might be 

 described as a peculiarly modified funnel-shaped pseudopodium. By direct 

 observation the author has further demonstrated that the collar, with its 

 characteristic currents, is an exquisitely contrived trap for the arrest and 

 capture of its customary food, which, driven by the action of the centrally 

 enclosed flagellum against the outer margin of the collar, adheres to it, 

 and passes with the onflowing protoplasmic stream into the animalcule's 

 body. The whole nutrient process, with its associated circulatory currents, 

 as exhibited by an animalcule of the solitary genus Monosiga, will be at 

 once comprehended on reference to the coloured illustration given in the 

 frontispiece. Now, what has been described and delineated of the inde- 

 pendent collar-bearing type Monosiga and its allies, is found to obtain with 

 full force, and in the very minutest detail, in the essential collar-bearing 

 flagellate units of a sponge-body. The collar there exhibits the same 

 circulatory motions and is subservient, in the self-same way, as a trap for 

 the capture of food-particles ; the body, as already intimated, exhibits the 

 same posteriorly located rhythmically pulsating contractile vesicles, the 

 same central spheroidal nucleus or endoplast, and presents, furthermore, 

 the most closely identical reproductive phenomena. The essential collar- 

 bearing sponge-monads, or Spongozoa, as they have been appropriately 

 designated by Mr. Carter, are, in fact, to all intents and purposes, collar- 

 bearing Flagellate Protozoa, differing only from Codosiga, Salpingoeca, 

 Desmarclla, and the various other genera included in this volume under 

 the denomination of the Choano-Flagellata, in their special colonial mode 

 of aggregation, and in the accessory and non-essential elements more 

 usually, but not invariably, added in the form of skeletal structures. 



An additional character, indicative of the close identity in all functional 

 manifestations that exists between the sponge-monads and the indepen- 

 dent collared types, remains to be mentioned. In the descriptions given 

 of these latter, attention is frequently directed to the extreme plasticity 

 of the individual animalcules, and the facility with which the funnel- 

 shaped collar and flagellum is retracted at w^ill, pseudopodium -like 

 extensions of the body-sarcode projected, and the most polymorphic 

 aspects exhibited. Examples of such metamorphoses, as presented by 

 the loricate type Salphigceca amphoridiuvi, may be seen at PI. V. Figs. 

 5-8, and also in many other figures illustrative of this genus, and the 

 illoricate Codosiga and ]\Ionosiga, in the several plates devoted to this 

 interesting group. Among the collared monads of the more complex 

 sponge-stock, not only an equal, but a far higher degree of plasticity 



