j^o THE ANIMAL KINGDOM. 



Another group of Conchifera arc the Stoneborers, 

 which excavate deep holes for themselves ; some of them 

 work in limestone, others exercise their industry on clay 

 or wood. 



The Ship -Worm (Fig. 104), however, restricts itself to 

 wood, and bores in every direction ; nor is it particular as 



Fig. 104. 

 THE SHIP-WORM. 



to the peculiar wood it attacks, for it can bore equally 

 well in the hardest oak as in common fir. 



Tunicata. These form another group of headless 

 Mollusca ; they receive their name from the circumstance 

 of their mantle forming not a shell, but a leathery coat 

 or tunic, which the animal inhabits. Some of them live 

 alone, whilst others are associated in compound masses, 

 but without any connection with each other. In another 

 group, such as the Social Ascidians, all the individuals 

 are connected by a sort of stem. Finally, the lowest 

 group of the mollusca is that called Polyzoa.* Almost 

 every one who has been at the sea-side will have met 

 with some of these in the form of the Flustra, or Sea- 

 mat, which consists entirely of masses of cells of a horny 

 texture ; and if this is examined by means of a strong 

 microscope, each cell will be seen to be inhabited by a 

 minute animal having long tentacles, with cilia (fine 

 hairs), all working away most vigorously to produce a 

 current in the water so as to bring food to its hungry 

 mouth. The following extract from Dr. Carpenter's 

 description of these animals will, I am sure, interest 



* Poly, many ; zoa, animals. The entire colony or assembly is termed 

 the " Polyzoary." 



