18 C<ELENTERATA. 



their embryological nor in their adult condition phenomena that 

 do not find their parallel among the simple unicellular Protozoa." 



The skeleton or internal framework of sponges is strengthened 

 either by calcareous, siliceous, or ceratose spicules of various forms ; 

 and a simple classification into three orders has been founded on 

 this character. It sometimes happens that a sponge, as Dysidea, 

 forms for itself a skeleton of spicules of other sponges or other 

 foreign substances. 



The Physemaria of Hackel are supposed to be sponges which 

 do not go beyond the Gastrula stage ; they have no pores and are 

 fixed. Carter and Saville Kent assert their foraminiferal nature. 

 Recently Eay Lankester decides Haliphysema to be an Amoeba 

 enclosed in a test of sponge-spicules. Norman forms of it an 

 order which he calls Psammoteichina. 



The common sponge of commerce is Spongia officinalis; the 

 freshwater sponge, Spongilla fluviatilis ; Neptune's cup, Raphio- 

 phora patera. 



Almost every one who writes on Sponges has a classification of 

 his own. Gray had at least three, the most elaborate (though 

 not the latest) being marked by the excessive multiplication of 

 genera, which, as he himself observes, are "founded on very dif- 

 ferent principles and characters" by different authors. Carter 

 has divided the Sponges into eight orders, including numerous 

 families and groups, the latter with hybrid and bizarre names, 

 Bowerbank into three, Schmarda into nine, and Glaus into two. 

 Hackel has three legions one of these, Calcispongise, is the subject 

 of a remarkable work. His method obliges him to sweep away 

 the old genera and to create new ones, whose names are drawn 

 successively by affixes from the representatives of his three 

 orders Ascones, Leucones, and Sycones. These are character- 

 ized as "spurious genera" by Norman, who observes that our 

 common Grantia compressa, with its varieties and "possible mo- 

 difications," has 28 generic, subgeneric, and subspecific names, 

 which might be further extended to 54. But all sponges are from 

 their "unlimited pliability" subject to perpetual variation, and 

 sometimes different form-species arise out of " one and the same 

 stock," " which, according to the usual system, would belong to 

 several quite distinct genera." 



The Calcispongiae Hackel affirms, " with the greatest certainty," 

 were developed from Olynthus. The "order Ascones" was the 

 first to develop, from which the Leucones and Sycones arose as 

 "diverging branches." 



The British species of calcareous sponges belong, according to 

 Hackel's nomenclature, to the following genera : Grantia com- 



