228 



Part III. — Twenty -fifth Annual Report 



Maturity and Spawning. 



Wilson says that the mussel may become ripe when one year old. 

 He found ripe sexual elements in mussels measuring g-inch in length. 

 At the Bay of Xigg one mussel which was |-inch long spawned. 



Mlntosh gives the spawning-time as lasting from April to June. 



Spawning of thb Female. — At the Bay of Nigg mussels were 

 observed to spawn on three occasions, viz. — (1) a mussel measuring 2J 

 inches on 6th April ; (2) a second of the same size on 1st June ; and (3) 

 two mussels measuring respectively |-inch and l|-inch on June 30th. 



Scott found that the mussels at Piel Laboratory spawned between the 

 beginning of May and the middle of July. The eggs were being dis- 

 charged some time before the sperms were observed, viz., 13th June. 

 The spawning of the eggs usually took place during the night, but he had 

 an opportunity of observing the manner in which they left the parent. 

 " The embryos flow from the female in a slow distinct current. When not 

 disturbed they settle down on the mud close to the parent as an obvious 

 pink mass." 



The mussel which spawned on 1st June had been brought from Klaksvig, 

 Faroe, by Captain Sutherland, s.t. " Pointer," of Aberdeen. It was 

 obtained on 1st May, and had been kept till May 31 in the basket in 

 w r hich the sounding-line is coiled. On being transferred to sea-water on 

 that date it was found to be alive. It was a very old-looking mussel, and 

 was covered with barnacles. Xext day a quantity of white stuff was 

 seen on the bottom of the vessel near the round end of the mussel 

 (fig. 84). This was found to consist of eggs and some stringy tissue. 



Spawning of the Male. — On June 30th the current of water was 

 stopped in a box in which there were some mussels, and in the 

 afternoon a greyish cloud was seen towards one side of the box and 

 extending to the surface. When a drop of Ihe water was examined it 

 was seen to be crowded with sperms. The sperm has a tapered point 

 and a very long tail (fig. 24). They rush about in circles with a 

 quivering, jerky, side-to -side motion. 



On 13th June Scott observed the discharge of the sperm. It was so 

 abundant that the water in the tank became quite turbid. 



Duration of Spawning. — Scott maintains that practically the whole 

 of the reproductive elements were discharged at one emission, extending 

 from one to three hours. The same animal did not again set free any 

 more reproductive elements. When such a spent mussel was opened and 

 examined the whole reproductive organ was found to have collapsed. 



This was not my experience in the case of the mussel that was brought 

 from Faroe. It first extruded eggs on 1st June, and it spawned several 

 lots up till June 5th. It may have, however, been a little irregular, 

 since the mussel had been kept under exceptional conditions. 



According to Mr. King, the mussels at Budle Bay, Northumberland, 

 spawn in July, August, and September. In warmer seasons they spawn 

 earlier, and vice-versa; 50°-60° F. is a fair heat in summer at Budle 

 Bay. Lebour states that " Mr. Mitchell finds that there are two breeding 

 seasons, one in Spring and one about August." Mr. Masson, Findhorn, 

 who attended the demonstrations to fishermen at the Laboratory in 1906, 

 informed me that in the river there the mussels empty [spawn] during a 

 spate, and then fill up again. R,ed mussels (female) w T ere more common 

 than yellow (male). At Montrose, Fullarton and Scott report that 

 " Mr. Johnstone was of the opinion that the mussel spats in May, June, 

 August, and the beginning of September, while others held that the 

 mussels spat all through the year." 



