4 PETER OKKELBERG 



fact that the temperature is higher in this part of the stream, 

 but it may also be correlated with the fact that many larvae 

 have been carried down stream during successive years of their 

 life, so that the number ready to transform into adults is greater 

 in the lower part of the stream. Evidence for this is the fact 

 that older larvae are usually obtained from the lower part of the 

 stream, while it is very seldom that any large or full-grown larvae 

 are found in the upper part. 



I have found that the males appear on the spawning grounds 

 before the females. Usually also only males are found in the 

 nests early in the morning and late at night. That the males 

 appear earlier in the season than the females was observed also 

 by Young and Cole ('00), and, according to Surface ('97), the 

 same is true of the lake lamprey. It is therefore necessary to 

 collect the animals when they are spawning under optimum con- 

 ditions in order to obtain reliable data concerning sex ratio. 

 Dean and Sumner ('97) report more males than females in the 

 proportion of five to one. It is easy to see how one might get 

 such results from collections early in the season or at certain 

 times of the day. Loman ('12) found no such disproportion of 

 sexes in the European brook lamprey and neither have I found 

 in the American brook lamprey an excess of one sex over the 

 other when spawning conditions were at their optimum. 



It is claimed by Loman ('12) that in the European brook lam- 

 prey internal fertilization takes place. The same idea has been 

 advanced by Ferry ('83) in regard to the marine lamprey. To 

 test whether or not spawning females of Entosphenus wilderi 

 contained spermatozoa, the urogenital sinus, as well as the pos- 

 terior portion of the body cavity, of a large number of living speci- 

 mens was examined. In no case could any spermatozoa be found, 

 nor did the eggs from the posterior part of the body cavity de- 

 velop without the addition of sperm after being stripped. This 

 shows clearly that, if internal fertihzation occurs m this species, 

 it must be only as a rare exception. The spermatozoa of the 

 brook lamprey are motile for less than a minute after being shed 

 into the water, but they are extremely active and are extruded 

 sunultaneously with the eggs. It is, therefore, inherently prob- 



