of the Fishery Board for Scotland. 



349 



( 4th batch of eggs deposited. 

 < 5th „ 15 seconds later. 



( 2nd short period of rest of 7f minutes' duration. 



{5th batch of eggs deposited. 

 7th 12 seconds later. 



8th „ 30 



3rd short period of vest of 9 minutes' duration. 



After five or six such spawning periods, there was always a long period of 

 rest extending over several hours. 



The eggs when first extruded are not quite circular, and the egg mem- 

 brane, not being fully distended, presents a wrinkled appearance. At this 

 time the eggs are slightly adhesive, and when collected in small clusters 

 cling to one another with considerable tenacity. Soon, however, an 

 inception of water takes place through the egg envelope, and the ova 

 gradually become fully distended and the egg envelope tense. The slight 

 adhesiveness of the egg envelope is then lost, and the eggs may be made 

 to roll about on the bottom of the tank by creating a current in the water. 



The number of ova extruded at one time appears to vary very consider- 

 ably, and I have no accurate data to give, as it was impossible to count 

 them. Speaking roughly, I should say the number varied from 30 to 200, 

 with perhaps an average of about 100. Supposing five spawning periods 

 to follow in rapid succession, separated only by a short interval (see pre- 

 ceding table), and that during this time 13 batches of ova were deposited, 

 this would give an aggregate of 1300 ova deposited in about 40 minutes. 

 The large female already referred to continued to shed batches of ova at 

 intervals for a period of eight or ten days. 



2nd period, 



3rd period, 



APPENDIX F.— No. XIV. 



ON THE PHYSICAL CONDITIONS OF THE WATER IN THE 

 FIRTH OF FORTH. By Hugh Robert Mill, D.Sc, F.R.S.E., 

 F.C.S., Chemist and Physicist to the Scottish Marine Station. 



The Firth of Forth may be taken as extending from Alloa to the 

 Isle of May. From Grangemouth to near Queensferry it averages 1J 

 miles in breadth, with a depth of less than 10 fathoms ; at Queensferry 

 it contracts to 1 mile, and the depth increases to over 40 fathoms, but 

 diminishes afterwards. From Queensferry the breadth increases to 5 miles 

 at Leith and 16 at Musselburgh. The Firth contracts to 8 miles at North 

 Berwick, and again widens, measuring 18 miles across where it merges 

 with the North Sea at the Isle of May. The deep water at Queensferry 

 is confined to a very small area, and the 10 fathom stream, broken by a 

 few deeper patches, runs along the northern shore to near Kirkcaldy, 

 where it widens out in a funnel shape (Plate XX.). A short tract of 

 over 10 fathoms, known as the Narrow Deep, lies to the south of 

 Inchkeith, and a few miles to the east of that island the 20 fathom area 

 begins as a narrow stream, trending north-eastwards, and spreading out 

 off Largo towards both shores. The Isle of May is connected to the 

 mainland of Fife by a submarine plateau rising to less than 20 fathoms 

 from the surface, and a few miles to the eastward of it depths of over 

 30 fathoms commence. The mean depth of the whole Firth is 14 fathoms, 

 the greatest extent of shallow water being the range from Leith to North 



