HALF AN HOUR WITH SEA-MATS AND SQUIRTS. 141 



with a strong lens. Before describing them in 

 detail, however, it will be as well to keep to our 

 plan of explaining, as briefly as possible, the position 

 of the group in the animal kingdom, and the charac- 

 ters which distinguish it. 



Fig. 71. 



Sea-Mat (Flustra hispida). Ditto, magnified. 



The magnified representation already given shows 

 the surfaces of the fronds to be covered with a net- 

 work of chambers. These chambers have walls of a 

 horny substance, in which there is often diffused 



