APHRODITA, PERIPATUS. ORDER TUBICOL^E. 305 



the lateral setee or bristles exhibit a beautiful structure, which 

 admirably fit them for weapons of defence, being barbed on each 

 side at their tips ; and each of these barbed setee is inclosed in 

 a smooth horny sheath, composed of two blades. Lastly, we 

 may mention a very curious genus, Peripatus^ which is probably 

 to be placed in this order, although it is a resident on land. In 



some respects it 

 bears a resem- 

 blance to the 

 lulidze ( 824), 

 having legs adapt- 

 ed for walking, 



FIG. 527 PERIPATUS IULIFORMIS. 



which present 



some appearance of articulation or jointing ; but in the softness 

 of its body, and in the termination of the legs in tufts of bristles, 

 it evidently corresponds with the Nereidans. 



ORDER II. TUBICOL^E. 



840. The animals of this order never attain to the same 

 dimensions with the preceding ; and more is known of the casings 

 which they form, than of the structure of the animals themselves. 

 One of the commonest of these is the shelly tube exuded by the 

 Serpula ; which is formed of calcareous matter, resembling that 

 of the shells of Mollusca, and apparently secreted from the sur- 

 face of the body in a similar manner. In fact, it is often scarcely 

 possible to distinguish between the shell of a Serpula and that of 

 a Vermetus (Fig. 583). The tubes of the Serpulse (Fig. 528) are 

 generally found clustering in masses, attached to the surface of 

 stones, shells, or other bodies, which have been immersed for any 

 length of time in the sea ; they are usually more or less contorted 

 in form, varying in this respect according to the position in 

 which they grow ; but they are always closed at one end, which 

 tapers to a point, the wide end being open to give exit to the 

 head and mouth of the inhabitant. The animal which forms 

 this shell, and resides in it, has its branchial filaments or gill- 

 tufts all assembled round the head ; where they form a pair of 



