2l6 REPORT OF THE COMMISSIONERS OF 



As the course of the stream where the beds abound is divided into pools, separated 

 by stony riffles or shallows, the nests must be made at the ends of the pools. Of the 

 spawning beds personally observed during several seasons, nine tenths of the entire 

 number were formed just above the shallows (at the lower ends of the pools), while 

 only a few were placed below them (see illustrations Nos. 8, 9, and 10). An advan- 

 tage in forming the nest above the shoals rather than below is that in the former 

 place the water runs more swiftly over the lower and middle parts of such a bed than 

 at its upper margin, since the velocity decreases in either direction from the steeper 

 part of the shallows; and any organic material or sediment that would wash over the 

 upper edge of the nest is thus carried on rather than left as a deposit. When formed 

 below the shallows, owing to the decreased velocity at the lower part of the nest 

 compared with that at the upper, the sediment is likely to settle in the hollow of the 

 nest, and, through the process of decay of the organic material, prove disastrous or 

 unfavorable for the developing embryos. 



The necessity of sand in the spawning bed indicates the explanation of why 

 we see so many shallows that have no spawning lampreys upon them, while there 

 are others in the same vicinity that are crowded. There will be no nests formed if 

 there is too little or too much sand, not enough or too many stones, or stones that 

 are all too small or all too large. The stones must vary from the size of an egg to 

 the size of a man's hand, and must be intermingled with sand without mud or rubbish. 



The lampreys choose to make their spawning nests just where the water flows 

 so swiftly that it will carry the sand a short distance, but will not sweep it out of 

 the nest. This condition furnishes not only force to wash the sand over the eggs when 

 laid, but also keeps the adult lampreys supplied with an abundance of fresh water con- 

 taining the dissolved air needed for their very rapid respiration. Of course, in such 

 rapid water the eggs are likely to be carried away down stream, but Nature provides 

 against this by the fact that they are adhesive, and the mating lampreys stir up the 

 sand with their tails, thus weighting down the freshly laid eggs and holding them in 

 the nest. Hence the necessity of an abundance of sand at the spawning site. 



Description of 5pawnincr Lampreys. 



The mature spawning lampreys (see illustration No. I, a and b) differ not only 

 internally but also externally from those that remain in the lake and are adult but 

 not sexually mature. All of the former of both sexes have a conspicuous swelling or 

 oedema at the base of the dorsal fin. This swelling is always present in both sexes 

 when they first swim up stream to their spawning grounds, and it is the only constant 

 external feature that characterizes the sexually mature lampreys of both sexes at all 

 parts of the running and spawning season. In their internal features they agree at this 



