Estimates of reproductive potentials are subject to variation of one kind or another. Counts of oviducal eggs or those in nests may be misleading, as in some individuals one or more eggs may have been deposited previously. Mitsukuri (1905:263), Newman (1906:135), Muller (1921:182), and Cahn (1937:183) have mentioned that the number of eggs per clutch corresponds to the size of the female. Females of northern populations may have larger clutches than females of the same size from southern populations.
Table 8. Records in the Literature Pertaining to Number and Size of Eggs of Three American Species of Trionyx.
Additional records of size of clutch are provided by data from dissected females ([Table 9]). All females were collected from May through September from localities south of latitude 36.5°. The number of eggs includes those in both oviducts, and the number of ovarian follicles those in both ovaries. The number and range in size of only the largest group of follicles is listed; in some instances the size of follicles formed a graded series, and the designation of a group was arbitrary.
Table 9. Length, Number of Oviducal Eggs, and Condition of Ovaries in Adult Females of T. spinifer and T. muticus.
| Species | Size of female (plastral length, cm.) | Eggs (total) | Ovarian follicles (total) | |
| Number | Size (mm.) | |||
| muticus | 14.4 | 6 | 14 | 15-18 |
| 16.3 | 9 | 4 | 15-17 | |
| 16.5 | …… | 3 | 16 | |
| 16.5 | 3 | 4 | 14-18 | |
| 17.2 | …… | 13 | 14-21 | |
| 27.0 | …… | 25 | 18-21 | |
| spinifer | 16.2 | 7 | 4 | 16-20 |
| 16.2 | 7 | 5 | 18-20 | |
| 16.2 | 7 | 1 | 18 | |
| 16.3 | 6 | 5 | 16-18 | |
| 16.3 | 4 | 5 | 15-19 | |
| 16.8 | 6 | 1 | 18 | |
| 17.3 | 3 | 2 | 17 | |
| 18.3 | …… | 13 | 19-20 | |
| 19.5 | …… | 2 | 17 | |
| 19.8 | …… | 4 | 20 | |
| 20.7 | …… | 11 | 15-18 | |
| 21.5 | …… | 6 | 8-11 | |
| 22.0 | …… | 13 | 11-14 | |
| 23.5 | 8 | 12 | 20-24 | |
| 25.5 | 11 | several | 18-22 | |
| 25.8 | 13 | ? | 18-21 | |
| 26.8 | 10 | 5 | 18-20 | |
| 30.5 | 13 | 5 | 20-21 | |
| 16 | 16 | 16-21 | ||
| 11 | 19 | 15-20 | ||
| 17 | 23 | 18-22 | ||
| 17 | 22 | 14-20 | ||
| 8 | 15 | 18-22 | ||
Published data ([Table 8]) indicate that the average number of eggs per clutch for the three American species is about 20, although the number of eggs may exceed 30 in spinifer and muticus. Except for those of ferox, most of these records are based on observations in northern latitudes (approximately 40°). My examination of females from southern latitudes (below 36.5°) reveals no oviducal egg count greater than 17 and an average number of eggs per clutch of 9.6 per spinifer ([Table 9]); that of muticus is 7.3, as based on data given in [Table 9] as well as on egg-nest counts of 15, 6, 6, 6, 6, [572] 5, 9, 8, and 8. Ovarian follicles larger than 15 millimeters in diameter are arbitrarily considered to comprise the next clutch that will be deposited in the current season. Follicles of this size possibly are retained until the following year or some may undergo regression; some of the included follicles may not be representative of the succeeding egg complement. The average number of follicles of the most enlarged groups is 9.0 for spinifer and 10.5 for muticus. Females in northern latitudes probably have a greater reproductive potential than those in southern latitudes if it is assumed that there is only one laying per season for an individual; the maximum number of eggs laid at any one time probably does not exceed 35. There is an indication that larger females deposit more eggs than smaller females ([Table 9]). Muller (1921:184) mentioned two double eggs (each having two yolks) in the complement of 33, indicating an abnormally large number and excessive crowding of eggs in the oviducts. Simkins (1925:188) also mentioned some eggs of a clutch (form and locality unknown) that were five or six millimeters larger (about 31-32 mm.) than the rest, and which "invariably bore twins." The largest number of eggs in a single nest mentioned by Simkins is 22. If the presence of double-yolked eggs is indicative of crowding of eggs in the oviducts, the egg complements of 22 and 33 indicate the approximate maximal number of eggs per clutch. In the species spinifer, the average size of sexually mature females is slightly smaller at some places in the south than in the north. Therefore, smaller clutches are to be expected in the south.
Many of the females collected in June or July contained corpora lutea four to eight millimeters in diameter in addition to enlarged ovarian follicles. Presumably the corpora lutea indicate clutches deposited earlier in the current season, and the enlarged follicles represent clutches to be deposited in the current season. One female of muticus (OU 27593) obtained on July 10, contains oviducal eggs, ovarian follicles 15-17 millimeters in diameter, and corpora lutea of different sizes that exceed the number of oviducal eggs; possibly this female was capable of laying three clutches each season. Corpora lutea, representing ovulation points of eggs in the oviducts, are approximately eight millimeters in diameter. In order to establish definitely the reproductive potentials of any species of turtle, it is desirable to know the approximate size of ovarian follicles that are retained by sexually inactive females, and the rate of regression of the corpora lutea. The data suggest that, in southern populations at least, two and possibly three clutches of eggs are deposited in the annual breeding season. Mitsukuri (in Cagle, 1950:38) found that T. sinensis deposited four groups of eggs each season.