g2 SPONGES 
CLASSIFICATION. 
I give below my idea of the division and arrangenient 
of the higher groups among sponges. 
SPONGES. PORIFERAE. 
Metazoan or egg-bearing animals, with three layers, 
(ectoderm. mesoderm and entoderm ) of deferentiated 
cells, prominent among which are the collar cells, and with 
or without hard skeleton. 
Class I. Calcareous Sponges. 
Skeleton always present and composed of spicules of 
limy matter. 
Class II. Silicious, Horny, and Fleshy Sponges. 
Skeleton present or absent, and when present is either 
composed wholly of spicules of silica or horny matter, sup- 
plemented with spicules of silica, or wholly of horny matter. 
