The ovaries of female cottonmouths examined revealed ova in various stages of development. In individuals less than 300 millimeters in snout-vent length the ovaries are almost completely undeveloped; in immature individuals from 300 to 450 millimeters in length the follicles are from one to two millimeters in length; in post-post females follicles vary in size, the largest being about seven millimeters. Reproductive females also contain follicles of various sizes. One or two sets are less than three millimeters in length, and large ova that soon are to be ovulated are present. Ovarian ova found in April ranged in length from 23 to 35 millimeters. No embryonic development was observed in most individuals until June or later.

TABLE 8.—Percentage of Gravid Females of A. p. leucostoma in 50 Millimeter Size Classes.

Snout-vent
length		 Number of
gravid females		 Total number
in size class		 Percentage
gravid
450-499 3 14 21.4
500-549 7 17 41.2
550-599 8 17 47.1
600-649 5 7 71.4
650-699 2 9 22.2
700-749 2 3 66.7
750-799 1 1 100.0
850-899 1 1 100.0
Totals 29 69 42.0

Increase in length of testes appears to be correlated with length of the individual rather than cyclic reproductive periods (Fig. 4).

Fig. 4. Length of testes in cottonmouths of various sizes
( ·—left; °—right ). The right testis is always longer than the left.

The reproductive cycle in cottonmouths resembles that illustrated by Rahn (op. cit.:237), in which the ovarian follicles of post-partum females begin to enlarge in late summer and autumn, with ovulation occurring the following spring. By means of retaining sperm successive broods possibly are produced after only one mating. In captivity, at least, some females may not follow this biennial cycle; Stanley Roth (M.S.), biology teacher in high school at Lawrence, Kansas, had a female of A. p. piscivorus, from Florida, that produced broods of 14 and 12 young in two consecutive years.

Embryonic Development

After ova are fertilized a three and one-half to four-month period of development begins which varies somewhat depending on the temperature. In almost every instance the ova in the right uterus outnumber those in the left. Embryos usually assume the serpentine form in the latter part of June and are coiled in a counterclockwise spiral with the head on the outside of the coil. At this time the head is relatively large and birdlike in appearance with conspicuous protruding eyes. Sex is easily noted because the hemipenes of males are everted. By late July scales are well developed and the embryo is more snakelike in appearance, but pigmentation is still absent. By mid-August the color and pattern are well developed, the egg tooth is present, the snake shows a considerable increase in size over that of the previous month, and much of the yolk has been consumed. Some females that contain well developed embryos also contain eggs that fail to develop. Sizes of ova vary irrespective of size of female and stage of embryonic development. Lengths of ova ranged from 22 to 51 millimeters in May to 35 to 49 millimeters in July and August. A two-yolked egg was found in one female.