262 THE PROPERTIES OF PROTOPLASM 



are probably descended from ancient forms of Reptilia or from forms 

 intermediate between the Reptilia and the Amphibia it is of interest 

 to note that many of the Amphibia and some of the Reptilia which 

 inhabit fresh water exhibit a low osmotic pressure of the blood-serum. 

 The following are illustrative figures cited after Hober and Jona. 



Lowering of 



Species. freezing-point. 



Amphibia: 



Ranaescuknta . . . , . 0.465 



Salamandra maculata 0.479 



Reptilia: 



Emys europaia 0.474 



Emydura macquariw 0.550 



Thalassochelys caretta 0.610 



It will be observed that the fresh-water turtle, Emys europaia, has 

 blood of which the osmotic pressure approaches the amphibian type, 

 the marine turtle, Thalassochelys caretta has the avian and mammalian 

 type of osmotic pressure of the blood, while the tortoise, Emydura 

 macquarice represents an intermediate pressure. The osmotic pressure 

 of amphibian blood-serum closely approaches in magnitude the pres- 

 sures obtaining in the eggs of birds. 



Among the various orders of Fishes in the Teleostomi or bony 

 fishes, which are phylogenetically the most recent and highly developed 

 forms, the osmotic pressure of the blood-serum approximates much 

 more nearly to that of the blood of Mammalia, Aves and Reptilia 

 than to the osmotic pressure of the ocean which the marine forms 

 inhabit. In the phylogenetically older and less specialized forms, the 

 Elasmobranchii or sharks, however, the osmotic pressure of the blood 

 approximates that of sea-water, as the following figures, cited after 

 Bottazzi, reveal: 



Lowering of 



Fluid. freezing-point. 



Sea-water 2.30 



Elasmobranchii : 



Torpedo marmorata .- . 2.26 



Mustelus vulgaris . . . . * . .-. . . 2.36 



Trygon violacea 2.44 



Marine teleostomi : 



Charax puntazzo 1.04 



Cernagigas . 1.04 



Crenilabrus pavo 0.75 



Box salpa 0.84 



Fresh- water teleostomi: 



Anguilla vulgaris 0.58-0.69 



Barbus fluviatilis 0.475-0.558 



Lcuciscus dobula 0.45 



Perca fluviatilis 1 



Cyprinus carpio [ n _ 



Tinea vulgaris ( 



Esox lucius 



In lower marine forms the tissue-fluids approximate still more 

 closely in composition and concentration to the sea-water which these 

 organisms inhabit. The following are results obtained by Bottazzi: 



