no ANIMAL LIFE 



shrimp a variety of breathing devices adequate to 

 the different demands of its members. 



To meet these varied exigencies two methods have 

 been elaborated with great detail. First, the con- 

 struction of a channel along which the oxygen-holding 

 water is made to flow, and, second, an increase in the 

 oxygen-holding power of the blood. 



The first of these methods is the secret of the 

 greater advance that the shrimp family has made 

 over that of the worm, and it is also the motive under- 

 lying the formation of the shells of the molluscs. The 

 buckler of a shrimp, lobster, or crab, the valves of a 

 mussel, are tubes confining the respiratory current 

 to a comparatively narrow area in which the gills lie, 

 and thereby increasing the rate at which the water 

 can be drawn over them. The second of these methods 

 is largely effected by pigment. Our blood we know 

 needs iron to keep it healthy, and it is a fact that gives 

 us new affinity with lower animals that in them also 

 the same ferruginous red blood is found. It occurs 

 in those which have to live where oxygen is scarce 

 or in parts of the body where muscular action is most 

 sustained. Elsewhere we find a copper salt taking the 

 place of the iron one, giving with oxygen not a red 

 but a blue tint, and possessing only a quarter of the 

 oxygen-holding power that belongs to haemoglobin, 

 its iron relative. Finally, in the less exigent forms the 

 blood is hardly more than a stream of watery albumen. 



The working of the first method is easily tested. 

 If some powdered carmine or indian ink is placed 



