SECT. I] PHYSICO-CHEMICAL SYSTEM 307 



aquatic species far outnumber the terrestrial ones; as Spenser 

 put it: 



O ! What an endlesse Worke have I in hand 



To count the sea's abundant progeny, 

 Whose fruitfull seede farre passeth those on land, 



And also those which wonne in th' azure sky: 

 For much more eath to tell the starres on hy, 



Albe they endlesse seeme in estimation, 

 Than to recount the sea's posterity. 



So fertile be the flouds in generation, 



So huge their numbers, and so numberlesse their nation. 



It might therefore be supposed that a much greater space would 

 have to be devoted to their eggs than what has already been taken 

 up, but this is not the case, for the bird's egg has been so convenient 

 a material for research that the knowledge we have of it outweighs 

 that of the eggs of all other animals put together. Indeed, the data 

 about the eggs of other groups are very fragmentary, so that much 

 caution has to be used in making comparisons, and general relation- 

 ships are much more difficult to enunciate. Van Beneden's classical 

 memoir may be recommended as an account of the morphology of 

 the eggs which are to be mentioned, and it is hardly necessary to 

 refer to Balfour's book on comparative embryology. 



If Table 30 is examined, and compared with Table 2, it will at 

 once be seen that the percentage composition of eggs of other classes 

 of animals differs markedly and in very definite ways from the egg 

 of the hen. The case of reptiles may first be taken, as being less remote 

 than others. The reptilian egg seems to be distinctly drier than that 

 of the bird, by about 20 per cent., and much more variable in its 

 fat/protein ratio. For, while in all birds' eggs that have been in- 

 vestigated, the amount of protein, whether related to dry or to wet 

 weight, is about the same as that of fat, the reptilian egg shows big 

 variations from this rule. In the eggs of the tortoise and lizard, for 

 example, there is twice as much protein as fat, while in those of the 

 grass-snake, studied by Galimard, there is three times as much fat 

 as protein. This fact will be mentioned again later (see p. 313). 

 Considerably more is known however about those of amphibia, 

 which have also been found to contain a great deal more protein 

 than fat. Thus, instead of the 40 per cent, protein and the 40 per 

 cent, fat which make up the dry substance of the hen's egg, Faure- 



