42 



conditions assumed by the simple collared monads, at 

 separate growth periods, and also that the reproductive 

 bodies or so-called ciliated larvae of the adult sponge-stock, 

 are but ovate aggregates of similar flagellated units.* 

 Viewed from this standpoint, a sponge body may be re- 

 garded as a colony stock of unicellular animalcules, or 

 collared monads, including individuals in every stage of 

 development, which throw off and live immersed within a 

 common mucilaginous matrix, and within which matrix is 

 built up, by a process akin to that of crystallization, the 

 spicular or other skeleton characteristic of the specific form 

 to which it belongs. In whichever way interpreted, either 

 as a tissue forming metazoon allied to the corals and all 

 higher invertebrate animals, or as a colonial protozoon, 

 or social aggregate of many thousands of the simplest 

 unicellular animals, the main structural points already 

 described, remain undisturbed, and may be appreciated by 

 the examination of any ordinary sponge, as prepared for 

 domestic use. Taking the finer Turkey cup-sponge by 

 way of example, all the minute perforations that traverse 

 the external surface, represent the areas or so-called 

 " pores," through which, during life, the food-laden currents 

 of water were drawn into the interior substance of the 

 sponge ; the wider orifices upon the interior surface of the 

 cup, on the other hand, represent the larger channels or 

 " oscula," by which the same water, having all previously- 

 contained nutritive particles extracted and laden in ex- 

 change with fcecal matters is finally discharged. In the 

 coarser variety, distinguished by the title of the bath or 



* An illustrated account of these collared monads so nearly related 

 to the Sponge, is included in the work, " A Manual of the Infusoria," 

 3 vols., by W. Saville Kent, F.L.S., F.Z.S., published in the years 

 1S81-82. 



