37 



plaice and dab. There is said to be enormous destruction 

 by the larger sea-birds. According to the fishermen who 

 gave evidence to the Commissioners of 1879, the decrease 

 in some cockle beds may be directly attributed to the 

 increase in sea-gulls due to the operation of the 8ea-Birds 

 Preservation Act. Whole cockle beds may be destroyed by 

 a bard frost or by an encroachment of sand. 



At the beginning of the year the reproductive glands 

 are nearly ripe, and spawning commences at the end of 

 February or the beginning of March. The spawning 

 period is prolonged, and ends about June or July. The 

 reproductive glands then pass into the " spent " condition 

 and after a short time begin to ripen again. Eggs and 

 milt are shed freely into the water, where fertilisation and 

 development go on. The minute larva swims freely in the 

 water for some time, then settles down in the sand as a 

 small shelled cockle. 



After a detailed account of the anatomy of the cockle as 

 a typical Lamellibranchiate Mollusc, an Appendix follows, 

 containing an account of the animal from the economic 

 aspect, with special reference to the cockle fisheries in the 

 Lancashire Sea-Fisheries district. 



The Shell. 



As in the case of most Lamellibranchs, the shell is 

 equivalve, that is, the two valves are precisely alike in 

 shape ; it is inequilateral, the straight central rib or groove 

 on each valve dividing it into unequal anterior and posterior 

 parts ; as regards the form and relative proportion of 

 the two parts so delimited, and the ratio of length to 

 lateral breadth or depth, great variability is found. The 

 number of ribs varies from 20 to 24. The external surface 

 is marked by a series of fine concentric grooves and ridges 

 indicatinjj; the growth of the shell margin. Some of these 



