1 6 Manganese in Land and Fresh Water Mollusca. 



anojther (v. concolor) most of the manganese was in the skin 

 (skin 16, liver i«8, rest 1*5) •* 



The significance of these data cannot be fully determined 

 without a good deal of further observation. It is, I think, 

 pretty clear that a certain quantum of manganese is not a 

 fixed and necessary constituent of the body for each species 

 of snail. The different results from the same species are too 

 variable for this. Thus, of the stagnalis from thirteen different 

 loci, eleven fall between I and 6, one gives 9 and one the unusual 

 figure of 29 ; in peregra from fourteen loci the variation is less, 

 from 1 to 10, but is still considerable ; among eight lots of 

 alliaria the highest is 99, the lowest 3 ; in twelve batches of 

 cellaria the range is from 3 to 71, and so on. In specimens from 

 the same locus the variability Is much less ; thus, twenty-five 

 specimens of Avion hovtensis collected in one place at the same 

 time were analysed in five lots of five each and gave 8, 11, 12, 

 12, 16 ; five lots of sowevoyi similarly treated, 11, 12, 14, 14, 14. 

 It seems unlikely, therefore, that the manganese in these snails is 

 in combination in the blood as a respiratory proteid such as the 

 haemoglobin described by A. B. Griffiths 2 in Pinna squamosa 

 in which manganese was found in quantity by Krukenberg 

 long ago. 3 If this were its office, one would certainly expect 

 the quantity to be more uniform. On the other hand, the 

 differences between different species are too large and too 

 regular to be due to ' accident.' If one compares, for example, 

 the Zonitidse with the Helicidse, there can be little doubt that 

 it is definitely characteristic of the former to have more manga- 

 nese than the latter ; of 45 analyses of Zonitidae, one falls as 

 low as 2, and in 38 of Helicidse only one rises as high. Similarly 

 Anodonta evidently has much ; Sphcerium little or none. 



It is an obvious suggestion that the differences found depend 

 upon differences in food, the intra-specific variation being due 

 to casual vagaries of eating, the inter-specific differences to 

 more regular dietetic habits. Our information as to the natural 

 foods of mollusca is very sparse, and the subject is not easy to 



1 The skin constituted 69 per cent, of the total dry weight and con- 

 tained 95 per cent, of all the manganese : in the other the figures are 

 66 and 61 per cent, respectively. 



2 Comptes Rendus, Vol. CXIV. (1892), p. 840 ; Proc. Roy. Soc. Edinb., 

 Vol. XVIII., p. 293 ; Physiology of Invertebrates, p. 145. 



3 Other objections to this view are that the moderately manganiferous 

 PI. corneus has much haemoglobin, and the highly manganiferous Anodon 

 and Unto are commonly said to have haemocyanin (O. von Fiirth, Chem. 

 Physiol, dev niederen Tiere, 1903, p. 105). I found no manganese in the 

 j uices of L. stagnalis. It has been supposed, but apparently on insufficient 

 grounds, that manganese is a necessary constituent of human blood, and 

 that its absence leads to a special form of anaemia (J. Gaube, Mineralogie 

 Biologique 1899, Vol. I., p. 161). 



Naturalist 



