215 



bath with 60 % caustic potash. The frozcD sections show that 

 the colour and intensity differ from month to month, although 

 the years do not repeat entirely the same conditions. The 

 liver is a lighter green about September, and it is certain that a 

 dark brown colour, much more intense than at other periods of 

 the year, appears in March and April, the months which cover 

 the reproductive period. 



MacMunn concluded that the colour was secondary in 

 nature and derived from the diatoms taken in food. List* and 

 Dastre and Florescof have shown that the liver can be colour- 

 fed. This organ of Mytilus certainly shows most colour 

 during the period of the plankton maximum and when the 

 spores of algae are abundant. It is interesting to note that 

 the amount of ash steadily increases up to the two months in 

 question ; since the amount of ingested sand and mud must 

 affect considerably the ash estimation, this also suggests 

 a vigorous feeding in the early spring. There is evidence that 

 the time of most active feeding is from January to April. J 



Composition of the Mussel Shell. 



Estimations for calcium carbonate and iron were carried 

 out on shells ground to a powder in a mortar, from various 

 samples. The water percentage was estimated from the 

 difference in the weights of a sample of powder before and 

 after drying to constant weight in an electric oven at 100° C. ; this 

 was carried out immediately after the grinding down of the 

 shells. To obtain the amount of calcium carbonate present, 

 a sample of approximately 0-5 grammes of shell powder was 

 taken, and dissolved in dilute hydrochloric acid, after the organic 

 matter had been removed by ignition in a crucible. The 

 solution was made alkaline with ammonia, and then acetic acid 



* List, " Die Mytiliden," Fauna und Flora des Golfe-s von Neariel, 

 XXVII, 1902. 



t Dastre and Floresco, C. R. Ac. Sc. Paris, T. 128. 



1 Herdman and Scott, loc. cit., p, 41. 



