The Ottawa Naturalist. 7 



inside these tubes is colourless, slightly opalescent, and contains the 

 characteristic corpuscles or floating cells present in all blood. This 

 description of the nutrient fluid applies not to Echinoderms only, it is 

 true, also, of mollusks, though there are some familiar exceptions. 

 Certain cuttlefishes have green or even violet blood, while in the familiar 

 Planorbis the blood is red. If from the simple dilated heart-tube of a 

 shell-fish, say Unto, or of a beetle or lobster, we take a little of the watery 

 blood, we may see, in the oxidised fluid, a faint blue tinge visible, due 

 to haemocyanin, which tinge disappears under deoxidation. When we 

 come to the vertebrates, the highest forms of animal life, we find in the 

 simplest and most primitive of them, the worm-like lancelet {Amphioxus), 

 colourless blood. Nay, in the early larval stages of other vertebrates, 

 such as fishes, the blood is at first colourless, and the corpuscles exhibit 

 no tint. Now it is well known that fishes, amphibians, reptiles, and 

 higher animals, possess a circulation, called the lymphatic system, in 

 which a clear corpusculated fluid flows. This lymphatic system is suffi- 

 ciently distinct from the arteries and veins to be regarded as separate ; 

 but its real importance has not been generally recognised. It is usually 

 regarded as a supplementary and subordinate system. In view of the 

 foregoing facts it would seem in reality that the lymphatic system repre- 

 sents the primary blood-circulation. Physiologists have long been 

 puzzled in interpreting the real nature of the red blood in man. The 

 red-corpuscles are certainly not true cells, as Dr. Minot has shown, and 

 they are not nucleated. The serum of red blood is almost identical 

 with the lymph, and the white corpuscles are believed to be neither more 

 nor less than lymph corpuscles or leucocytes originating in the lympha- 

 tic glands. The red-blood system has thus overshadowed the colourless 

 blood, or lymphatic system, in man and the highest vertebrates, and 

 the latter system has been, to some extent, turned to other purposes ; 

 the lymphatics of the digestive canal being now lacteals for conveying 

 chyle into the red-blood system. 



In the lower vertebrates the lymphatics still play an important part, 

 and retain much of their primitive character. In fishes, well-marked 

 pulsating chambers or lymph hearts, connected with an elaborate system 

 of capillaries and larger vessels, convey clear lymph fluid and floating 



