36 



The Spawning of the Mussel (Mytilus edulis) . 

 (J. Johnstone.) 



During the last year an investigation of the reproductive 

 organs of the common Mussel has been made in relation 

 to the period during which spawning takes place on the 

 beds along the Lancashire sea coast, and to the histo- 

 logical changes accompanying the ripening and extrusion 

 of the reproductive products. The methods employed 

 were : — (1) The microscopic examination of the gonads of 

 specimens taken by Mr. A. Scott from the Roosebeck scars 

 and the beds in the Barrow Channel, and of specimens sent 

 by the bailiffs from the Wallasey, New Brighton, and 

 Morecambe beds ; (2) the search for free-swimming and 

 fixed larvae on the beds themselves, and (3) the examina- 

 tion of the in-shore tow-nettings taken by Mr. Wright in 

 Morecambe Bay, and by Mr. Eccles outside the estuary of 

 the Mersey. The records of a continuous weekly series of 

 tow-nettings, taken in the year 1895 by Mr. B. L. Ascroft, 

 at Lytham Pier, have also afforded valuable evidence. 



As a result of this year's observations, it has been found 

 possible to fix approximately the date of a maximum in 

 the spawning of the Mussel, during which a rapid and com- 

 plete extrusion of the genital products, accompanied by 

 other histological changes in the mantle and visceral mass 

 of the animal, takes place. In the year 1898 this was 

 found to begin about the beginning of July and last till 

 about the beginning of August ; but it is probable that the 

 limits of this period are variable to some extent. There 

 is, however, considerable doubt as to whether this is the 

 only time in the year during which spawning takes place, 

 and various observations render it at least possible that 

 there is a secondary spawning period early in the year, 

 and that there is a continual but slow emission of ova and 



