384 Hilda Khicaid : 



The results show several interesting features: — 



1. Taking the class Invertebrata as a whole it will be appa- 

 rent from the table that the protective or skeletal tissues derive 

 their physical properties of rigidity, etc., from mineral matter 

 other than phosphate, the latter only being present in small 

 amount : the chief mineral salt being calcium carbonate. When 

 a tissue is composed largely of calcium carbonate, this salt is 

 invariably crystalline, and in consequence the tissue is brittle. 

 Calcium phosphate on the other hand is capable of existing in 

 a colloidal form, which does not render a tissue brittle. Appa- 

 rently then the Invertebrates as a whole have not learned to 

 avail themselves to any extent of colloidal calcium phosphate in 

 the construction of their protective tissues ; thus whilst they 

 are rigid they are at the same time easily broken. 



2. Taking the individual groups of the Invertebrata it is 

 most interesting to note an increase in the PoO- content of 

 the exoskeleton as we ascend the evolutionary scale. Thus the 

 Sponges, the Hydrozoa, the Corals, and the Polyzoa, have 

 merely a trace of P:,0,, as evidenced by a yellow coloration 

 and a faint haze of precipitate with ammonium molybdate 

 and nitric acid. Then the Starfish has a measurable quantity — 

 .26-30 per cent. In the group Arthropoda we find a marked 

 rise, particularly in the fresh-water " yabbie " or Astacopsis, but 

 not so marked in the salt-water crayfish, falling again to a low 

 percentage in the oyster shell and cuttle fish of the next group, 

 Mollusca. Some authors, however, would give the Arthropoda 

 a higher place than the Mollusca, in evolution, and in regard 

 to the utilisation of phosphorus in the exoskeleton they are 

 certainly further on than Mollusca.. 



F. — Experiments to determine the DisTRiBrTioN and Evolu- 

 tionary SIGNIFICANCE OF PHOSPHORUS IN THE EnDOSKELETON 



OF THE Vertebrates. 



In all the experiments in this section the bone analysed was 

 the femur or that most comparable to the femur ; thus in 

 fishes the bone supporting the pelvic fin was the one used. 



Results follow in tabular form : — 



