962 THE AMERICAN NATURALIST. [Vor. XXXIV. 
probable errors, we need discuss only the larger collection of 
827 statoblasts. 
The mode is 13, the range from r1 to 21; or, omitting the 
single statoblast with 21 hooks, the range is 11—19 (Figs. 1-6). 
Statoblasts from Fresh Pond, Cambridge, Mass., are stated by 
Hyatt to have had, in 1866, 12-17 hooks; and those of 
Pennissewassee Pond, Maine, 20-22 hooks. The statoblasts 
of Pectinatella magnifica which Kraepelin found at Hamburg 
varied like those at Fresh Pond, 12-17. 
The mode lies over toward the lower limit of the range; 
consequently the mean lies above the mode and the skewness is 
rather large, + 0.077.! The index of variation (e) is rather large 
as compared with that of other integral variates. The coefficient 
of variation (c) is also large as compared with that derived from 
some graduated variates, as the following series shows : 
CUM INDEX Mu COEFFICIENT 
us OF VARIATION. OF VARIATION. 
Rays of dorsal fin, Acernia EO V 2 0.6040 14.16 4.266 
Müllerian glands of swine ....... 1.6808 3.50 48.009 
Rostral teeth Patent varians .. 0.8627 4-31 19.999 
Height of U. S-vecruits -o 2.5848 in. 67.30 in. 8.689 
Height of St. Lonis sociis aged 8 5.5524 cm. |118.27cm. | — 4.698 
Length-breadth index, Bavarian skulls 3.468 mm. | 83.07 mm. 8.621 
Length right human ¢ nini: Es 23.72 mm. 452.28 mm. 5.425 
Length right radius human 9 — 10.95 mm. | 214.86mm. 5.096 
Angle of neck of femur with shaft . . 5:578? 124.26° 4.469 
Maximum length of clavicle? .... 9.208 mm. | 136.85mm. 6.724 
- Sacral Whee Pe ee 9-353% 115.000% 8.137 
Scapular mier, e eee 3.815% 65.900% 8.575 
Infra spinous index of scapula... . . 8.572% 89.454% 9.893 
! For comparison I introduce some skewness determinations of other qualities : 
PN T Weldon’s crab measurements, “ No.4?” . . . + .077 
Baxter's height of 25,875 recruits, U. S. 2) 035 
iS * Porter's height of 2192 St. Louis schoclghds (U.C o AMI 
x * goo Bavarian skulls: length-breadth index. . . + -032 
M * dorsal teeth of Palemonetes varians . . + . + +130 
Pearson & Filon, '98, Müllerian glands of swine . . . . - T3! 
scd v ge lower valve. . . noan . à » «. 0045 
nppet " . . «+ 0.0000000058 
? The first three data are derived from counting. T They are integral variates. 
In them we see that the index of variation is more constant than the coefficient 
