50 Roosevelt Wild Life Bulletin 



connection it should be recalled that all of the observations made 

 during the summer of 191 9 demonstrated just the reverse, the leeches 

 being much more plentiful in the body of the lake aboA-e the old dam 

 than below it. This was attributed to their not having yet migrated 

 in large numbers into the newly filled lower end of the lake. Some- 

 time during the inten'al between the two examinations this redistri- 

 bution has taken place. Nevertheless, in 1920 they had failed to 

 attain in the new part of the lake their abundance of the preceding 

 year in the old part. Their distribution had become much more 

 uniform but the population was nowhere so dense as in the most 

 populous places in 1919. 



If these rather meagre though consistent data can be relied upon 

 it appears clear that the total population of MacrohdcUa in Carr" 

 Pond has been considerably reduced, for not only do the figures 

 indicate that the ratio of decrease in the old part exceeds that of 

 increase in the new part of the lake but it must be remembered that 

 the area involved in the former is about four and one-third times 

 that involved in the latter condition. How much of this decrease 

 may rightly be attributed to the effects of the experiment and how 

 much to other conditions it is impossible to know, inasmuch as, 

 unfortunately, no definite checks could be made available. It may be 

 pointed out, however, that the differences in hydrography of the tsvo 

 parts of the lake is consistent with a greater destructive effect of 

 freezing in the old than in the new section. In the former is found 

 more of gently shelving beach and large areas of shallow. The 

 lowering of the water level exposed some fairly extensive fiats upon 

 which the wintering leeches must have found it difficult to escape 

 the effects of the cold. On the other hand most of the new part of 

 the lake has a trough-like form with the bottom in most places sloping 

 rapidly into deep water. Not only would this conformation retard 

 the chilling process but it would facilitate the escape of the leeches 

 from its effects. The removal of the old dam, permitting of a freer 

 circulation of the water and doubtless of a freer interchange of life 

 also, doubtless facilitated the migration and equalization of the 

 leeches in the two parts of the lake. 



The time was insufficient for any careful determination of the 

 relative abundance of other life associated with the leeches during 

 the two summers. But I was strongly impressed that frogs were 

 much less plentiful in 1920 than in 1919. This seemed especially so 

 on the shallows near Globe and Brooklyn Industrial Camps. At all 

 points around the shore except one area near the dam the marginal 

 vegetation was obviously less luxuriant than in 1919. 



In view of the facts and opinions recorded in the foregoing 

 account it was very desirable that the experiment be repeated. Con- 

 sequently in a letter to ^Ir. Welch, under date of August 18, the 

 following paragraph was written : " It seems to me that the results 

 are sufficiently encouraging to warrant a continuance of the experi- 

 ment and I recommend that the water be again lowered during the 

 coming winter with the same precautions emphasized in my 

 memorandum of last year, and in addition that the degree of lower- 



