CONTRIBUTIONS FROM THE ZOÖLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE, E. L. MARK, DIRECTOR, No. LXXIII. STUDIES IN MORPHOGENESIS, VI. A CONTRIBUTION TO THE QUANTITATIVE STUDY OF CORRELATED VARIATION AND THE COMPARATIVE VARIABILITY OF THE SEXES. BY C. B. DAVENPORT AND C. BULLARD. Presented October 14, 1896. THE following quantitative study of variation is based upon counts of the Müllerian glands of the fore legs of 4,000 swine. Our attention was directed to these glands as favorable objects of study by Gertrude Crotty Davenport, who had already collected some data concerning their variability. These data, together with valuable suggestions derived from her own experience, she generously placed at our disposal. The positions of the Müllerian glands are indicated upon the wrist by large openings or pits, about 1 mm. in diameter, which are found only upon the inner aspect of the fore legs. The number of pits is variable. Where there are several they occur, for the most part, in a single row trending somewhat obliquely to the long axis of the leg. In no Of the 8,000 legs examined, the arrangement of the glands was studied on only 2,000 legs, 1,000 male and 1,000 female. The total number of glands on a single leg varies from 0 to 10. When the number is large, some of the glands are frequently found outside the main row. case have we found more than nine glands in one row. We may call those lying outside the main row lateral glands. The lateral glands usually (six exceptions) occur at the upper (proximal) end of the series. Their number does not usually exceed two, but in a single case we have found four. These four glands lay in a secondary row parallel to the main row, which contained five glands. In one other case, where three lateral glands were found, these lay parallel to the main row of five. When there are two glands they may lie either in a line parallel with the main row, or make any angle up to 90° with it. Lateral glands occur more rarely when the total number of glands on the leg is small, but we have found one extreme case in which the only two glands on the leg occurred side by side, i. e. in a transverse row. The reduction in the number of glands takes place from one end, the distal end of the series. Generally, where there are only two or three glands these occur high up and the normal diatance apart. Rarely, however, the reduction is brought about in part by the failure to develop in the middle of the series while glands develop near the extremes, so that there is a broad hiatus in the series. Since the proximal end of the series is that at which glands are most likely to be formed, and since they tend to be produced more abundantly there, this end, which occupies the region of the upper wrist, is to be considered as the source of the morphogenic impulses which give rise to the glands. Sometimes the embryonic Anlage does not develop beyond this point; sometimes, on the other hand, it develops along the whole extent of the wrist in one row, and even forms an accessory "lateral" row. The total number of swine examined was, as stated, 4,000; of which 2,000 were males and 2,000 females. The total number of fore legs examined was, accordingly, 8,000; 4,000 left and 4,000 right. All of the observations fall, consequently, into four groups of 2,000 cases each; namely, male right, male left, female right, female left. These four groups will be considered, for the most part, separately. We first determined how many legs in each of these classes had no glands, one gland, two glands, and so on. The results are given in the following table. No. of Glands. 0 TABLE I. 。 1 2 3 4 5 6 7 8 9 1 10 Total. In the following table, which is based upon the preceding, the numbers are all reduced to per milles. The two lines of totals are here, accordingly, replaced by means. A glance at this table shows a close parallelism between the distribution of glands in the four cases. 7.5 112.5 176.5 218.5 205.5 148.5 77.5 39.0 8.0 6.0 0.5 7.0 120.5 168.0 215.0 214.5 147.5 79.5 26.5 15.0 5.0 1.5 Mean ♂ ? R L 7.2 116.5 172.2 216.8 210.0 148.0 78.5 32.8 11.5 5.5 1.0 7.5 104.5 182.5 241.0 207.0 138.5 67.0 36.0 11.0 4.0 1.0 10.5 106.5 180.5 219.0 216.0 144.0 74.5 34.5 8.0 5.5 1.0 Mean? 9.0 105.5 181.5 230.0 211.5 141.3 70.7 35.2 9.5 4.7 1.0 Mean of 8.1 111.0 176.8 223.4 210.7 144.7 74.6 34.0 10.5 5.1 1.0 and ? Several interesting questions now arise: (1) How closely similar is the average number of glands in the two sexes, and in the right and left leg of the same sex? (2) Which sex shows the greater variability, and to what extent is it greater? Is the relation between the variability of the right and left legs closer than that between the two sexes? (3) How closely correlated are the numbers of glands on the right and left legs of individuals? That is to say, what are the chances that a swine which has 2, 4, or 7 glands on the right leg will have the same number on the left leg also? 1. The Relation between the Abundance of Glands and the Sex or the Side of the Body. The average number of glands on a leg of either sex is determined by dividing the total number of glands counted in that leg by the number of individuals of that sex, in this investigation 2,000. This gives us the following result: |