SECT. 12] GYCLOSES, PHOSPHORUS, SULPHUR 1249 



Birge, Kemmerer & Robinson show that for Wisconsin lake waters, 

 while the dissolved phosphorus may occasionally rise to a typical 

 marine level such as 0-015 mgm. P per litre, it may often be com- 

 pletely absent, and in most cases amounts to about 0-003 mgm. P per 

 litre. Miiller again finds hardly detectable traces in the water of 

 Lake Balaton in Hungary. Thus the phosphorus requirements of de- 

 veloping marine eggs may be an important factor prohibiting their 

 colonisation of lake and river waters. 



Phosphorus entering an echinoderm egg from sea-water must do 

 so in the form of orthophosphate. Bertolo, using Pollacci's histo- 

 chemical reaction (which is said to give a blue coloration with all 

 phosphorus compounds, but which in fact only does so with inorganic 

 phosphate) , found with Strongplocentrotus and Sphaerechinus eggs that a 

 blue zone was produced round the periphery. If this observation has 

 any physiological meaning, it must be that the concentration of in- 

 organic phosphate is greatest at the periphery, as would be expected 

 if it were being absorbed through the surface and then turned into 

 something else. Herbst, in his work on the development of echino- 

 derms in artificial saline environments, at first stated (see p. 1273) that 

 phosphorus in the form of calcium phosphate was necessary for normal 

 differentiation and assumed that it was absorbed by the eggs. In a 

 later paper, however, he reported that perfectly normal development 

 would go on in the complete absence of phosphorus and attributed 

 his previous results to the precipitation, and hence the detoxication, 

 of traces of copper in his distilled water. Loeb about the same time 

 also reported that the eggs required no phosphorus from sea-water. 

 Both these workers, however, relied on tests of inferior delicacy, and 

 it is probable that under the conditions used by them, ample phos- 

 phorus was available for the developing eggs. 



Returning now to Table 1 76, it can be seen that two methods were 

 used, the first of which (plaster of paris) included the phosphorus of 

 the spicules in the plutei, while the second (trichloracetic acid) did 

 not. Accordingly they give different results from which it can be seen 

 that the phosphorus of the spicules is quite appreciable in amount, 

 being in fact about equal to the total phosphorus taken in from the 

 environment, and almost all in inorganic form. Prenant regards 

 echinoderm pluteus spicules as composed of calcite, and this is 

 especially relevant since calcite originates fi-om an amorphous form 

 of calcium carbonate which tends to be stabilised in the presence of 



