CHAPTER III 



SPONGES l 



PHYLUM PORIFERA. 



CLASS I. CALCAREA (CALCISPOXGIAE). 



GRAI>E 1. HOMOCOELA. 

 2. HETEROCOELA. 



CLASS II. HEXACTINELLIDA (HYALOSPONGIAE). 



Order 1. Lyssacina. 

 2. Dictyonina. 



CLASS III. DEMOSPONGIAE. 



GRADE 1. TETRAXONIDA. 

 Order 1. Carnosa. 

 2. Tetractinellida. 



GRADE 2. MONAXOXIDA. 

 Order 1. Halichondrina. 

 2. Hadromerina. 



GRADE 3. KERATOSA. 

 Order 1. Dictyoceratina. 

 2. Dendroceratina. 



GRADE 4. MYXOSPONGIDA. 

 (No Orders.) 



I. INTRODUCTION. 



THE Sponges or Porifera form a well -characterised group of 

 animals, very abundant in all seas, from the equator to the poles, 

 and flourishing at all depths, from the shore-line to the profoundest 

 abysses. One family (or sub-family), and, so far as is known, one 

 only the Spongillinae has established itself in fresh water, and is 

 represented by a great variety of genera and species in all parts of 

 1 By E. A. Minchiu, M.A., Professor of Zoology, University College. London. 



