51 



(3) of active formation of the genital products, ending late 

 in the spring, after which ova and spermatozoa are formed 

 less rapidly. A slow emission of these now goes on until 

 in the summer, about June or July, the maximum spawn- 

 ing period of the Mussel occurs. 



It is unlikely that any great proportion of the larvae 

 found during the course of the year are spawned otherwise 

 than at the maximum spawning period in the summer 

 months. We have seen that it is probable that a certain 

 proportion are spawned during the first half of the year, 

 but that these probably result from the spawning of 

 isolated individuals or from the slow emission of ova and 

 spermatozoa prior to the act of spawning proper, and the 

 fact that this occurs does not materially affect the general 

 statement that the Mussel spawns in the summer. For 

 the year 1898 we have fixed this spawning period as 

 having occurred during July, but it is probable that it 

 is variable, and as the Committee's bye-law fixes the 

 months of May, June, July, and August as those during 

 which it is illegal to take Mussels from the beds in the 

 district, it is very probable that, notwithstanding some 

 considerable variation in the occurrence of this period, it 

 will always fall within that close time. Probably spawning 

 is very generally over before August begins, but of this 

 further evidence is wanted. 



Explanation of the Plates. 



Plate I. 



Fig. 1. Dissection of an adult Mussel to show the external 

 opening of the gonad. The right valve has been 

 removed, and the right gill and mantle lobe cut 

 away close to the junction with the visceral mass 

 and reflected upwards. Full size. « — fS indicates 

 the plane of the section shown in fig. 2. 



