36o THE UNFERTILISED EGG AS A [pt. iii 



the normal sea water has twenty times as much sodium as potassium, 

 fish eggs often have quite twenty times as much potassium as 

 sodium. There would not appear to be in this connection any dif- 

 ference between homoio-osmotic and poikilo-osmotic aquatic animals. 

 It is also obvious from Table 47 that aquatic eggs often have very 

 much less salt in them than the ambient medium, and this would 

 be a special case of the phenomenon found in all marine animals, 

 and termed by Fredericq "Mineral hypotonicity". Bialascewicz 

 arranged the animals he studied in a list of ascending concentration 

 of metalHc ions as follows : 



which would also be an ascending table of taxonomic groups, were 

 it not for the high metal content of the echinoderm eggs, which 

 exceed even the fishes. 



There are other points concerning the relative amounts of salts 

 in the eggs which require mention. McCallum, who had for a long 

 time previously been studying the proportion of salts in the ash of 

 animals and parts of animals with reference to the composition of 

 sea water both now and in earlier geological epochs, made an 

 analysis of herring's eggs in 1926. He had previously differentiated 

 between palaeo-chemical salt ratios in bloods, namely, ratios re- 

 sembling that which pre-Cambrian sea water can be calculated to 

 have possessed, and neo-chemical salt ratios, namely, ratios resembling 

 the sea water of the present day. Thus Limulus polyphemus and Aurelia 

 flavidula, the king-crab and the medusa, which have always been 

 marine animals, now approach the modern sea in the composition of 

 their vascular fluids, but the lobster Homarus americanus, the selachian 

 Acanthias vulgaris, the frog, dog, and man, for instance, all have ratios 

 resembling the composition of the sea water at the appearance of 

 the protovertebrate form. He had also identified the kidney as the 

 organ responsible for maintaining the palaeo-ratios in the salts of the 

 blood. In order to explore the possibility of identifying a palaeo-ratio 



