The Cylcostomes, or Lampreys 499 



stream) there is nothing but sand. Farther up-stream are 

 found pebbles and stones commingled with sand, which com- 

 bination satisfies the demands of the lampreys for material 

 in constructing nests and covering eggs. The accessibility 

 of these sites, together with their suitable conditions, render 

 the inlet the great and perhaps the only spawning stream of 

 the lake; and, doubtless, all the mature lampreys come here 

 to spawn, excepting a few which spawn in the lower part of 

 Six-mile Creek, a tributary of the inlet. 



"As the course of the stream where the beds abound is 

 divided into pools, separated by stony ripples 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. An advantage in forming the nest above the shoals 

 rather than below it 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 which 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 



