IIo PORIFERA., 
Luspongia has only horny fibres, hence its skeleton is 
used for domestic purposes. Spongilla is a little fresh- 
water sponge, found in lakes and rivers. In many, like 
Luplectella (Venus’ flower-basket), the siliceous spicules 
welded together make a beautiful network like spun glass. 
The external form and habitat of Sponges have infinite variety. Very 
few, like -lscef¢a, retain their simple axial symmetry. Large colonies 
of indefinite shape are produced, in which the constituent individuals can 
only be recognised by the number of oscula. A remarkable little 
sponge (C/zova) forms burrows in oyster shells, and a great number 
of sponges are commensalistic (see Chapter IX.). Chondrocladia shows a 
remarkable protective resemblance to a bleached skeleton of a gadoid 
fish, ¢.g., a cod, while others have more or less similitude to stones and 
seaweeds. 
PHYLUM PORIFERA. 
1. Multicellular organisms, with physiological division 
of labour between the cells. ya! Metazoa. 
2. Sexual reproduction. 
3. Axially symmetrical. 
4. A central cavity (paragastric) with inhalent pores and exhalent 
osculum. 
5. A skeleton of calcareous, siliceous or fibrous nature. 
6. Mostly marine and sedentary, forming colonies. 
Class I.—CALCAREA. Class II.—Non-CALcCaREa. 
Type—Sycandra. Type—LEuspongia. 
1. Skeleton of calcareous spicules. | 1. Skeleton of siliceous spicules, 
horny fibre or none. 
2. Large collar-cells. 2. Small collar-cells. 
3. Mainly Ascons and Sycons. 3. Complex systems of canals. 
