THE SPONGES. | 139 
have there called Archispongia, arose out of the Protascus 
by the formation of pores through its body-wall; the 
primary form of Sea-nettles, which I there called Archydra, 
developed out of the Protascus by the formation of nettle- 
organs, as also by the formation of feelers or tentacles. 
The main-class or branch of the Sponges, Spongie, or 
Porvfera, lives in the sea, with the single exception of the 
green fresh-water Sponge (Spongilla). These animals were 
long considered as plants, later as Protista; in most 
Manuals they are still classed among the primeeval animals, 
or Protozoa. But since I have demonstrated their develop- 
ment out of the Gastrula, and the construction of their 
bodies of two cellular germ-layers (as in all higher animals), 
their close relationship to Sea-nettles, and especially to the 
Hydrapolyps, seems finally to be established. The Olynthus 
especially, which I consider as the common primary form of 
calcareous sponges, has thrown a complete and unmistak- 
able light upon this point. 
The numerous forms comprised in the class of Spongise 
have as yet been but little examined; they may be divided 
into three legions and eight orders. The first legion consists 
of the soft, gelatinous Mucous Sponges (Myxospongie), 
which are characterized by the absence of any hard 
skeleton. Among them are, on the one hand, the long-since- 
extinct primary forms of the whole class, the type of which 
I consider to be the Archispongia; on the other hand there 
are the still living, gelatinous sponges, of which the Halisarca 
is best known. We can obtaina notion of the Archispongia, 
the most ancient primeval sponge, if we imagine the 
Olynthus (see Frontispiece), to be deprived of its radiating 
calcareous spiculz. 
