204 THE BIOLOGY OF THE SEA-SHORE 



As a matter of fact, Putter, whose views on nutrition we have 

 discussed elsewhere, holds the behef that these frequent 

 reduplications of the body surface among invertebrates are 

 concerned rather with the absorption of food materials in 

 solution from the sea-water, than with respiration. Apart 

 altogether, however, from Putter's views, we still have to 

 take into account the fact that the so-called branchiae are 

 almost invariably covered with cilia which, in some cases 

 at least, undoubtedly serve to drive food particles towards 

 the mouth, e.g. the cephalic " gills " of tubicolous worms, 

 the " gills " of bivalve molluscs. 



A very comprehensive research into the question of 

 respiration in Polychaets has been undertaken by Bounhiol 

 (1902), and has provided data of much interest. With 

 regard to the significance of the numerous extensions of the 

 body surface so characteristic of this group, Bounhiol is 

 of the opinion that in the great majority of cases the term 

 " gill " is physiologically incorrect and should no longer 

 be employed. True branchiae occur only in the highest 

 types of the Errantia {e.g. the Eunicidae) and of the Sedentaria 

 (Arenicolidae and Terebellidae). 



The following analysis of the factors capable of influenc- 

 ing respiration in Polychaets is given by Bounhiol : 



Normal factors 



permanent 



transitory 



Accidental factors 



Physical : light, tempera- 

 ture, pressure. 



Morphological : size, de- 

 gree of organisation. 



Biological : habitat, mode 

 of life. 



Sexual maturity, meta- 

 morphosis. 



Changes in salinity. 



Our chief concern in this chapter is the effect upon 

 respiration of the special conditions of the sea-shore. We 

 wish to know, for instance, what are the special respiratory 

 modifications which enable certain shore animals to carry 



