6 PETER OKKELBERG 



Schaffner ('02) makes the following statement concerning the 

 age of Entosphenus wilderi at sexual maturity: "The larvae 

 taken a few days preceding the breeding season can be grouped 

 under three divisions as regards size, and we took this to indi- 

 cate that it required three years for the complete development 

 of the larvae." The sizes ranged as follows: Those almost fully 

 developed, 17 to 20 cm.; a second group, 9 to 11 cm.; and a third 

 group, 3 to 6 cm. 



The variation in size of the larvae of each year (figs. 1 to 4) 

 is so great that from any one catch a continuous series may be 

 selected. The measurements of seventy-seven adult males 

 taken at random show a range in total length from 13.5 cm. 

 to 19 cm., and an average length of 16.12 cm. Similar measure- 

 ments of sixty-five females give a range from 13.3 cm. to 18.5 

 cm., with an average length of 15.61 cm. It thus appears that 

 size is so variable in the adults and larvae of this species that it 

 cannot be regarded as a reliable index of the age of the individual. 



I have sought, by means of average curves, to determine the 

 length of the life-cycle in Entosphenus wilderi. Such curves 

 were obtained from measurements of the lengths of larvae col- 

 lected during single months of the year. When the number of 

 specimens was small, the sizes graded into each other so that no 

 suggestive curves were obtained. The greatest number of speci- 

 mens was collected in the month of August, and the curve repre- 

 sented in figure 1 is the result of measurements of 167 larvae 

 from this period. The first hump of the curve, with its peak at 

 2 cm., represents larvae hatched in the preceding April, and, 

 therefore, about four months old. Most of these larvae are about 

 2 cm. long. The second hump has its peak at 5 cm., and pre- 

 sumably represents larvae which are about one year and four 

 months old. The third, fourth, and fifth humps with their 

 peaks at 8, 12, and 18 cm. presumably represent larvae 2§, 3f , 

 and 4| years old, respectively. The larvae of the latter age 

 would undoubtedly transform into adults during the fall, as 

 they have already attained their full larval size. 



Another series of larvae from the month of February was 

 measured and the results are represented in the curve shown in 



