no PORIFERA. 



Euspongia 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 

 Eupledella (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, Uke Ascetta^ 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/ioiia) forms burrows in oyster shells, and a great number 

 of sponges are commensalistic (see Chapter IX. ). Chondi'ocladia shows a 

 remarkable protective resemblance to a bleached skeleton of a gadoid 

 fish, e.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. KAU Metazoa. 



2. Sexual reproduction. J 



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. 



Type — Sycandra. 



I. Skeleton of calcareous spicules. 



2. Large collar-cells. 



3. Mainly Ascons and Sycons. 



Class IL — Non-Calcarea. 

 Type — Euspongia. 



1. Skeleton of siliceous spicules, 

 horny fibre or none. 



2. Small collar-cells. 



3. Complex systems of canals. 



