6 



to decide upon the position and nature of the spawning 

 pond, in order that it may be completed in time for the 

 following season. 



Mr. Johnstone's work at Liverpool has been partly 

 the investigation in the Laboratory of any specimens 

 that were sent to us, partly assisting me in the 

 work, and partly (with Mr. Tom Mercer) looking after 

 the Fisheries Museum, and the Circulating Fisheries 

 Exhibition now at Preston. A good deal of Mr. 

 Johnstone's time in the Laboratory has been taken 

 up with the examination of Mussels and other shell-fish, 

 at all times of the year, and from various parts of the 

 district. The evidence as to the spawning habits of the 

 Mussel obtained from the microscopic characters of the 

 reproductive organs is rather puzzling, but it now seems 

 most probable that the Mussel commences to produce 

 mature reproductive elements in the middle of winter,* 

 and continues to emit eggs and sperms in small quantities 

 for the first six months of the year (probably in increasing 

 amount after April), during which time large eggs are 

 always to be found in the ovary ; and then, in the middle 

 of summer, produces rapidly a much greater number of ova, 

 so as to clear out the contents of the ovary, which suddenly 

 (about end of July) undergoes a great change, easily 

 recognisable under the microscope as the " spent " con- 

 dition. It then, after a brief interval, proceeds to develop 

 fresh ovarian tubules, and load up rapidly with young ova, 

 which develop during the autumn and early winter in 

 time to be mature at the end of the year. The full details 

 of these changes in condition will be found in Mr. John- 



* We have obtained Mussels with completely formed active spermatozoa 

 in the middle of December. Mr. Ascroft has found the free-swimming larva 

 at Lytham in April and May, and the first "strikes" of young Mussels 

 are frequently found here upon Algse in June. 



