vations made at the contrasted dates, and that in both instances the proportional lengths are nearly the same for the three species compared. Leg bones from frogs of the socalled "Zurich series of 1898." These frogs had been carefully fixed in 4% formaldehyde and then preserved in 80% alcohol. The effect of this on the lengths of the several leg bones was not at the time determined. (See Donaldson '08, p. 127). (D) PERCENTAGE VALUE OF THE LENGTH OF THE ENTIRE CENTRAL NERVOUS SYSTEM-THE TOTAL LENGTH OF THE FROG BEING TAKEN AS THE STANDARD. In the case of this character we have grouped the 1904 data (see Donaldson '08, table 5) into three entries and added the measurements on the new material for the 1909 groups. The table shows that the length of the entire central nervous system is slightly greater in the European species. As this excess in length is associated with a deficiency in absolute weight, it follows, as was previously noted (Donaldson '08, p. 128) that the nervous system in R. pipiens must exceed that of the European species in its transverse diameters. TABLE 9 Percentage value of the length of the entire central nervous system—the total length of the frog being taken as the standard (E) THE WEIGHT OF THE CENTRAL NERVOUS SYSTEM Turning now to the main character under consideration, the weight of the central nervous system, the condensed records are presented in table 10. When these data are put in the form of a chart, (chart 2) several interesting relations between the observations of 1904 and those of 1909 at once appear. In the first place the later records follow the same line as the earlier; second, the record for each species in 1909 is somewhat less than in 1904, and as a consequence still further below the records of 1904 for R. pipiens. This result serves to establish the main conclusion, namely that R. pipiens has a heavier nervous system than either of the European forms. The fact that the values for the weight of the central nervous system in the European species as determined in 1909 are less than those determined in 1904, calls for a word of comment. Some unpublished studies which are being made on R. pipiens at the Wistar Institute relative to the change in the weight of the central nervous system with season, indicate that in this species the greatest weight is attained about the end of July. If this observation applies, as it probably does, to the European species, then the differences in weight as shown in chart 2 are susceptible of the following explanation: The esculenta of 1904 were examined August 1-5, when it may be assumed that the nervous system of R. esculenta had attained approximately its maximal seasonal weight. In 1909 the examination was from July 5-7, or some four weeks earlier. Under these circumstances, a somewhat smaller weight was to be expected, and the records show this. The temporaria of 1904 were examined July 11 and 12, before the central nervous system had reached the maximum for the season. In 1909 the examination was from August 17 to 21, or some three weeks after the assumed maximum, and at a time when the seasonal weight has begun to diminish. Here the difference is less than in the case of the esculenta, but is susceptible of a similar explanation. The relation of these two series of observations can be conveniently shown in still another way. I have been able to point out (Donalsdon '02) that a fairly accuate determination of the weight of the central nervous system in frogs can be made by the formula. where C. N. S. is the weight of the central nervous system, Bd. W. the body weight in grams, L the total length in mm. and C. a constant to be determined for each species. Since publishing this formula I have found that the most convenient way of expressing seasonal variations on the weight of the central nervous system is by the variations in C. Applying this method to the series before us, and remembering that the increase in the relative weight of the central nervous system is measured by the increase in C, and vice versa, we obtain the following: |