Leeches 



49 



Table showing number of MacrohdcUa decora collected or seen 

 at selected stations (figure 3). Numbers 8 to 11 are on the new- 

 part, the others on the old part of the lake. Note that in 1919 the 

 number decreases with the progress of the season at every 

 station but number 11, though -this is less marked at stations 

 close to swimming- docks, as numbers 3, 7 and 12. X, means 

 no or incomplete collections made. 







Dates of Collections in 1919 





Aug. 



4 ands 



1920 



NUMBER AND LOCA- 

















TION OF STATION 



July 



July 



July 



Aug. 



Aug. 



Aug. 



Aver- 





5 



8 



14 and IS 



I and 2 



9 and 1 1 



21 and 23 



age 

 1919 





I. Island opposite Globe 



















Camp 



*23 



X 



13 



18 



II 



9 



14.8 



8 



2. Head of cove north of 

















Globe Camp 



X 



8 



7 



8 



7 



4 



6.8 



X 



3. Head of cove south of 



















Brooklyn Industrial 



















Camp 



6 



X 



7 



4 



2 



5 



4.8 



X 



4. Site of former sawmill, 















south end 



18 



X 



ID 



II 



8 



8 



II. 



7 



5. Head of cove south of 





Herbert's shack .... 



12 



X 



9 



7 



8 



9 



9. 



8 



6. Point north of Her- 



















bert's shack 



4 



X 



S 



6 



3 



3 



4.2 



X 



7. Shallow at Kennedy- 



















House Camp 



19 



X 



14 



14 



II 



13 



14.2 



6 



8. Shallow between the 



















Negro (Ideal) and 



















Ramapo Camps .... 



X 



8 



8 



8 



5 



4 



6.6 



X 



9. West shore near dam. 



















This area was prac- 



















tically all water . . 



6 



X 



4 



I 



3 







2.4 



7 



10. Pool at foot of dam. . . 



X 



2 



4 







X 



X 



2. 



X 



II. Foot of Nathan Hale 



















Camp. Proximity of 



















bathing beach 



X 



6 



7 



7 



6 



8 



6.8 



12 



12. North of Jacob Riis 



















Camp. Trinity Camp 



















1920, near crib 



X 



7 



9 



9 



8 



3 



7.2 



X 



* Some boys from Globe Camp assisted in making this collection. 



Stations (especially Nos. i, 4 and 7) on the old part of the lake all 

 show a very marked diminution in the number of Macrohdella col- 

 lected. These also are the points where this species was most 

 abundant in the summer of 1919. Possibly the fact that the first 

 collections recorded for 1919 were made between two and three 

 weeks earlier in the season may have exaggerated the divergence but 

 later collections made early in August (either the first or second) of 

 1919, within two or three days of the 1920 dates, give figures still in 

 excess of the latter (except for station 7), namely, 18, 11, 7 and 14 

 respectively for these same stations. Stations 9 and 11 are repre- 

 sentative of conditions on the new part of the lake and both exhibit 

 marked increases. 



Less thorough examinations and collections were made at many 

 other points and generally in the old part, and in nearly every case 

 in the newer part of the lake the results proved consistent with the 

 above figures, namely, they indicate that these leeches have diminished 

 in numbers in the old lake and increased in the extension. In this 



