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Notes on the Development of Mytilus edu/i's and 

 Alcyonium digitatum in the Plymouth Laboratory. 



By 



Annie Matthews, M.Sc. 



1. Mytilus edulis. 



No very definite statement has yet been made as to the time when 

 Mytilus edulis spawns at Plymouth. However, in 1911 records of 

 spawning in the Laboratory tanks were made in January, February, and 

 March, and in 1912 two specimens removed from the tanks spawned 

 in early May. 



Between May 10th and 21st, 1912, 100 mussels from Plymouth Pier 

 were kept in a Laboratory tank, but as they did not spawn they were 

 then opened, and many found to be either spent or only partly ripe. 

 Examination of samples brought in between May and August seemed 

 to indicate that the spawning season was finished, and occurred there- 

 fore in the early spring. 



Various attempts were made at artificial fertilization from apparently 

 ripe members of the selected hundred, but in one case only was 

 fertilization successful — May 21st. A piece of ripe ovary and of ripe 

 testis were shaken about in separate finger-bowls containing "outside " 

 water, and thus ripe eggs and spermatozoa were freed in the respective 

 bowls. At 12 noon a few drops of water containing spermatozoa were 

 added to the finger-bowl containing ova, and at 4 p.m. that day many 

 of the ova were developing — some showing Polar Bodies, others the 

 early segmentation stages. Next morning the ciliate trochospheres 

 were swimming at the top of the water in the finger-bowl, and these 

 were removed with a pipette to two small " Breffits " * containing 

 outside water, to which a few drops of a Nitzschia culture were added. 

 Development gradually proceeded, the velum at this time being of very 

 large relative size, and as Wilson states (" 5th Annual Keport Fishery 

 Board for Scotland, 1886-87"), the shell muscles and alimentary canal 

 are now elaborated, the valves of the shell being finely pitted and 

 almost semicircular in shape. 



However, while Wilson states that his larvae (now twelve days old) 



* Wide-mouthed jars of green glass of about 2 litres capacity. 



