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Part III. — Seventh Annual Report 



which were found during the famine years of 1782 and 1783 * at Tongue, 

 at Kiltnuir Easter, at Tain, and on the island of Sanday, and' were regarded 

 as ' almost a miraculous supply,' were placed within reach of the starving 

 people by the agency of the sea invading with its ponderous artillery com- 

 paratively sheltered spots. In this we may find an explanation of the great 

 quantities of recent shells which carpet the exposed beaches of the 

 Hebrides, and it may be that the occurrence in certain geological zones f of 

 countless bivalve fossils are as much due to the prolonged and destructive 

 action of the sea, as to the obliteration of individuals and species by the 

 movements of the earth's crust and alteration of the level of the land, or 

 by a sudden change in the physical conditions. Marine action may also 

 furnish a clue to the destruction of shallow-water bivalves in our seas, and 

 account in part, at least, for the scarcity of bait on the East Coast. 



The exposed nature of the East Coast, and the want of suitable harbours 

 are consequences of the character and age of the geological strata of the 

 shore, and of the nature of the rocks in the drainage area of the rivers. 

 With the character of the coast-line is correlated the distribution of the 

 bait-beds. These only exist in such sheltered places as are to be found in 

 the estuaries of the rivers, and the common scallops, with no mode of 

 attachment and requiring a depth of about 6 to 12 fathoms, flourish in such 

 protected areas as we find in the Forth. 



The adductor muscle is the most important organ of the scallop to the 

 fisherman, and when the fisherman divides the scallop so as to obtain two 

 baits the division is made by a longitudinal vertie d cut through the ad- 

 ductor and other organs. The organ next in economic importance is the 

 mantle. It is a thin and transparent covering enveloping the body and 

 lining the valves of the shell. Along its outer margin it is much thickened 

 and beset with about forty iridescent circular organs on each mantle 

 lobe. These iridescent organs are called 1 ocelli ' or ' eyes ' and structur- 

 ally resemble some other molluscan eyes, and certain stages in the develop- 

 ment of vertebrate eyes, but whether they perceive light many persons are 

 doubtful. In breathing and feeding the valves are slightly separated, the 

 opening of the shell being protected from the ingress of foreign matters by 

 a fold of the mantle of either side which is beset with a series of tentacular 

 cirri. These tentacular processes, along with the minute cilia which line 

 certain parts of the body and the labial palps set up currents of water 

 carrying oxygen to oxygenate the blood of the mantle and of the gills. In 

 these currents the food is borne to the mouth, which is situated underneath 

 the hinge at the anterior end of the shell. The gills, two pairs of which 

 are situated on either side of the body inside of the mantle, and the 

 mantle lobes constitute what the fishermen call the 'beard.' Sexual pro- 

 ducts are formed in distinct generative organs. The sexual organs are 

 situated alongside of and behind the rudimentary foot, the ovary and testes 

 being found in the same individual, occupying, however, different parts 

 in the post-pedal mass. As the contents of the ovary ripen the colour of 

 the hinder portion of the 1 abdomen ' or ' tongue,' as the fishermen call it, 

 assumes a brilliant red colour. When the ovarian products are shed the 

 ovary loses its red hue and becomes of a light brown colour. In February 



* Statistical Account of Scotland (Sir John Sinclair's), 1791-9, iii. 391, 396, 522; 

 iv. 300; vi. 185; vii. 497. 



+ In the mussel band of the carboniferous the fossil mussels lie horizontally, and the 

 two valves are still united at the hinge, showing that the molluscs were cast on shore 

 and buried alive. Had they been buried in situ, they would be found in their 

 natural vertical position, or had they died before being enclosed the valves would be 

 separated by the destruction of the ligament. In the Crag formation, on the other 

 hand, the shells died before being covered, and in this are in striking agreement with 

 the shelly boaches of the present day, such as Broad Bay, in the island of Lewis. 



