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Part III. — Twenty-fifth Annual Report 



The mussels examined in the Laboratory have been obtained from two 

 sources mainly, viz., from Mr. Allan, mussel merchant, Torry, and from 

 the sides of the pond at the Bay of Nigg. The description of the mussels 

 may be conveniently taken under the denomination of the month, and, 

 beginning with September, that arrangement will be followed. 



September. — The mussels obtained from the side of the pond were 

 fat, and had in the majority of cases yellow-coloured mantles. This 

 colour appears to be due to fat. One or two had thin dark-orange mantles ; 

 they are probably spent, or mussels that had not yet fattened. 



From a lot supplied by the merchant, two fat mussels were examined. 

 In one the mantle was cream-coloured ; in the other it was much paler. 

 Under the microscope very small spherical corpuscles were seen along with 

 broken ground tissue. One or two of the corpuscles had a slight 

 motion. 



November 19, 1906. — Some mussels measuring up to lg inches in 

 length were obtained from the walls of the upper reservoir tank. They 

 were in poor condition, with translucent mantles. The two sexes were 

 distinguished with difficulty. Two different classes were noted — one in 

 which the mantle and the abdomen were of a yellow colour ; the other 

 in which the same parts are slightly orange-coloured. Brown veinings 

 are seen in the mantle of the latter. These brown veins are lined with 

 cilia, in parts at least, and are filled with brown corpuscles, which, vary- 

 ing in size, debouch from the cut ends of the canals. There are also in 

 the tissue of the mantle little colourless ovoid bodies which, under a high 

 power, are seen to consist of several cells enclosed in an envelope. Under 

 medium and low powers the groups are egg-like. In the other mussel 

 the canals are, by reflected light, of a light yellow colour ; by transmitted 

 light they are dark. They are wide, and packed with small round cells. 

 When pressed out of the canal they are accompanied by small oscillating 

 corpuscles. There are numbers of small cells between the canals 

 differently arranged from the former mussel. 



November 27, 1906. — Mussels were obtained from the big pond. 

 They are fat, and show various conditions. Some of them had white 

 mantles. These, certain local fishermen considered to be better for bait 

 than the yellow mantle. They regard the yellow mantle as indicating 

 spawning. 



There were mussels showing mantles of intermediate shades of colouring 

 between the white and deep yellow or cream. The white and light 

 cream mantles have colourless veining. Others, dark cream in colour, 

 have brown veinings and amber spots. In one large mussel the mantle was 

 of a light cream-colour, with amber-coloured veins, and it had its surface 

 mottled with amber. The amber colour is due to minute amber-coloured 

 cells of various sizes, some of them being fairly large oval cells with 

 nuclei. There is also present a great quantity of refractive corpuscles. 

 In the case of the deep-cream mailt? e } the ground is white with an amber 

 mottling developed over it. In the light-cream mantle the brown cells 

 are absent, but clear cells containing what resemble the heads of sperms 

 were observed. The veining and mottling are rather colourless. 



November 19, 1906. — The mussels supplied were principally fat, with 

 heavy thick mantle, white or yellow in colour. Some small mussels had 

 pale thin mantles coloured brown, showing brown veinings with little 

 brown corpuscles. The white mantle when teazed out showed clear 

 round cells with large nucleus and pitcher-like cells crowded with small 

 refractive corpuscles mixed with small fat corpuscles. Great numbers of 

 small refractive corpuscles were free. The veins were colourless. A 



