THE COASTS OF SICILY. 267 



of the Artlculata and Mollusca, no trace of vessels 

 can be detected. The general movements of the 

 animal communicate motion to the liquid which is 

 enclosed between the walls of the body and the 

 intestine, and sometimes more or less irregular cur- 

 rents are produced by vibratile cilia, arranged in 

 bands or groups ; but there is no heart to give a 

 definite impulse, no arteries to distribute the nu- 

 trient fluid to the surface of the body, nor veins to 

 return it to the centre of the organism. In this 

 case there can be no distinction between arterial and 

 venous blood, or between lymph and chyle; and 

 here the liquid, which fills all the organic interstices, 

 receives the products of digestion directly and imme- 

 diately. 



In some cases the intestinal apparatus compen- 

 sates by a very singular arrangement for this absence 

 of circulatory organs; for we find this apparatus 

 charged with the duty of distributing to all parts 

 of the body the nutrient elements, which it is 

 specially destined to prepare. In these cases, we 

 perceive that it is complicated by the presence of 

 prolongations or appendages which reach the most 

 distant points of the organism. In the Nymphon 

 and the Pycnogonum — crustaceans which bear con- 

 siderable resemblance to certain field spiders — the 

 intestine penetrates to the very extremities of the 

 feet and claws, very much in the same way as if, 

 in man, the stomach were to be prolonged across 

 the neck, arms, and legs, to the jaws, wrists, and 

 ancles. 



Nature is much less economical of her forces than 



