268 



DETAILED DIRECTIONS FOE COLLECTING AND STUDYING SPECIMENS. 



The following directions and explanations have been prepared for the students 

 at the Biological Station for the study of the variation of the inhabitants of lakes 

 Turkey and Tippecanoe and the small lakelets in the neighborhood. 



1. Collect at random all available specimens, to the number of several hun- 

 dred, the last week in June, in both Turkey and Tippecanoe lakes, keeping the 

 exact location where each lot of specimens was collected. 



It is necessary to collect at random or the personal element of the collector 

 may become a disturbing factor in determining the variation. The date, which 

 is not necessarily fixed for any particular week, has been selected because at this 

 time many very young specimens, but a few weeks old, can be secured. It is 

 necessary to collect in both lakes at approximately the same date in order to se- 

 cure corresponding ages. 



2. Collect in the same manner and an equal number of specimens in each 

 lake near the end of August. 



From this second collection the rate of growth and any elimination taking 

 place early in life may be determined. 



3. Arrange the material of each date according to the size, to determine 

 whether the broods of successive years can be separated. 



If specimens have been collected at random and include all sizes this can 

 usually be done for the preceding few years. Among the older individuals the 

 gradation in size is usually too perfect to permit any groupiug according to age. 



4. Determine the variation in two or more prominent characters in each 

 brood of specimens, keeping the record and labeling the specimens in such a way 

 that the specimen for any record can at any time be re-examined. Determine at 

 the same time the sex. 



This is by far the m^st laborious and time killing operation, but absolutely 

 essential to determine anything further. The characters measured in fishes can 

 always be the number of rays in the dorsal and anal fins, and the number of scales 

 in the lateral line. Other characters will vary with the species, as one species has 

 one, another a different character that lends itself especially to the study of varia- 

 tion. In reptiles deviations in the number and characters of plates are available 

 characters for the study of variation. Of course any character can be takeD, but 

 one in which the variation can be numerically expressed and the number be deter- 

 mined by a simple count instead of a measurement, is vastly superior, since 

 nothing can be left to the judgment, and the personal element is therefore much 

 less important. 



