lsize bodywt brainwt
1      3   9.45   0.444
2      3   9.78   0.436
3      4   9.15   0.417
4      4   9.61   0.429
5      5   8.85   0.425
6      5   9.61   0.434
7      6   8.30   0.404
8      6   8.54   0.439
9      7   7.40   0.409
10     7   8.34   0.429
11     8   7.04   0.414
12     8   7.25   0.409
13     9   6.60   0.387
14     9   7.26   0.433
15    10   6.30   0.410
16    10   6.66   0.405
17    11   7.18   0.435
18    11   6.13   0.407
19    12   5.45   0.368
20    12   6.05   0.401