of the Fishery Board for Scotland. 233 



tank was tinted with the colour. It was first noticed at 11 a.m. 

 At 8 p.m. it was still to be seen, but more generally distributed. A cur- 

 rent of water had been steadily flowing into and out of the tank. 



Spatting. — Several specimens of modiolus, obtained in February 1907, 

 were kept alive in aquaria at the Laboratory. The water flowijig out of 

 these passed into the big pund. On July 17 some twigs which had been 

 put into the pond on April 25, 1907, for the purpose of collecting spat 

 were found to have yuung modiolus attached. Some were also attached to 

 the cord by which the twigs were anchored. The following are the 



«i7o« nf tViP vmHTtr • ^ i i _^_ _3_ 3 1 J 1 5 h_ 5_ 5_ _5 _5 



blZv-b Ol llie yUUUj,. .^^, g, g, ^g, j g, y^, ^, ^, ^, y^r, yg, y j. , y^, j ^, j ^r, 



r5> T6' tV. tV. -1%. T%. 8' 8. 8. i. T6- '^^^y ^ere, at most, five months 

 of age. They were regularly scattered over the branches of the twig, 

 and had attached themselves, no doubt, just at the end of the pelagic 

 stage. They had not been attached three months. If the pelagic stage 

 does not last more than a month, these horse-mussels must have been 

 under four months of age. 



The possibility of their having entered the pond by the inlet from the 

 sea may be neglected, since, so far as I am aware, modiolus has not been 

 found near the Bay of Nigg. 



The young modiolus were put into a box, which was covered with a 

 lid to exclude the light ; some were still attached to the twigs, others 

 were free on the bottom of the box. On September 2nd some of the 

 latter had climbed up the side of the box to the surface of the water ; 

 others remained attached to the twigs or on the bottom. 



The Growth of the Mussel {Mytilus edulies). 



Observations bearing on the growth of this shell-fish and its behaviour 

 under certain conditions have been made on mussels of different sizes that 

 have been kept in the Laboratory for from one to two years. 



One lot of mussels had been taken off the rocks at St. Andrews. 

 They measured about 1 to 1| inch in length. Obtained in July, 1904, 

 they were kept in aquaria with a constant run of water till April 6, 

 1905, when they were examined. They appeared then to be in good 

 condition, though not very fat. 



On July 4, 1905, some mussels taken off the rocks were measured, and 

 three lots were separated. 



In A they all measured y^^ inch in length 



„ C „ ,, about 1| „ „ 



They were put into vessels supplied with a steady run of sea water. 

 Mud gradually accumulated on the bottoms of the aquaria until a fairly 

 thick layer was formed. Now and then this deposit was removed. 



A. — On March 8, 1906, the mussels of lot A were measured ; their 

 lengths were found to be ^, y\, \, and 9 were slightly over y\ inch 

 long. 



When examined on August 5, 1906, the mussels were found to be all 

 of a peculiar shape, roughly barrel-shaped. They were broad laterally, 

 convexly curved above, concave below. Their sizes were — |, -f^, y^^, f, 



3 3 J_ 1 

 ¥> ^> 16» 1^- 



On Feby. 25, 1907, the measurements were — y^^, y^^., |, -^, J^, y%, y^r, 

 tV» h xfi- The largest was attached to the side of the aquarium a little 

 above the bottom ; the others were in the mud. 



