ARENICOLA; PERIPATUS. ORDER TUBICOLA. 301 



The Arenicola is one of the Annelides most distinguished by the 

 red colour of its circulating fluid ; and this colour is peculiarly seen 

 in the branchial tufts, which have a beautiful crimson hue during 

 the life of the animal. 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 lu- 

 lid(808),hav- 



PIG. 628. PERIPATUS IULIFORMIS. . 



ing legs adapted 



for walking, 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 is evidently allied to the Ne- 

 reidans. It forms the family PERIPATIDA:. 



ORDER II. TUBICOLA. 



911. The animals of this Order never attain to the same 

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

 which they form, than of the structure of the animals them- 

 selves. 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 se- 

 creted in a similar manner. In fact, it is often scarcely possi- 

 ble to. distinguish between the shell of a Serpula and that of a 

 Vermetus (Fig. 672). The tubes of the Serpulae (Fig. 629) 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 



