Lampreys frequently spawn at exactly the same places year after year. The location of these places is determined by shade, depth of water, swiftness of current, and barriers. The water temp. at the time of spawning lies between 10 and 11[degree] C. There is some segregation of the ammocoetes, due to the washing out of larvae from sites where the current is swift and their accumulation in protected situations provided with a richer food supply. Thus a high proportion of the older larvae has a greater growth rate. Evidence from frequency curves indicate a larval period of 3.5-4 yrs. and a total life span of 4 of 5 yrs. The rate of growth in length is greatest during the first 1.5 yrs., declines during the following yr., and increases again in the final stages. The relation of wt. to length does not follow the cube law. Increase in wt. up to a length of 120 mm. is less than the cube of the length, while beyond this point it is greater. The change of form is most marked during the phase of rapid growth. The difference in the value of the weight-length coefficient for fully grown ammocoetes and adults indicates that a reduction in length occurs at sexual maturity.