The Zoologist/4th series, vol 3 (1899)/Issue 701/On the Spawning of ''Bombinator pachypus'' after Two Years of Captivity in England, Monk

by J.L. Monk

 

ON THE SPAWNING OF BOMBINATOR PACHYPUS
AFTER TWO YEARS OF CAPTIVITY IN
ENGLAND.

By J. L. Monk.

 

The difficulty with which Batrachians are brought to breed in confinement, whether kept indoors or in the open, is well known to all who have attempted to study the habits of this interesting class of animals. It is also generally believed that when once the annual discharge of the genital products has been interrupted by captivity, the individuals are for ever barren. For example, the Xenopus lævis in the reptile-house at the Zoological Gardens bred in the year of their arrival, but in no subsequent year could they be induced to do so.

The case I have the pleasure of putting on record is therefore a most interesting one. Some specimens of Bombinator pachypus, captured by my friend Mr. Boulenger in Belgium in the early spring of 1897, before the breeding season had set in, have been kept in an aquarium for two years, when it was ascertained that, although pairing repeatedly took place, no spawn was ever deposited. Having placed them this spring in a small pond in my garden at Forest Gate, they have, to my surprise and satisfaction, paired and spawned under my eyes; and I append some notes on the observations I was able to make on this occasion, which may be acceptable to the readers of this Journal, since, apart from the late naturalist, Héron-Royer, no one has yet been able to ascertain with anything approaching precision the number of eggs that are laid by one female in the course of the breeding season.

There were two pairs of this species, the females both in breeding condition; but only one of the males appeared animated with genesic ardour, showing himself most constant in his attentions, not only to his legitimate mates, but even to a small Rana temporaria sharing the same pond.

The first spawn was deposited on July 3rd, one hundred and nine ova, in small bunches of two to ten, adhering to the weeds. There was an imperfect albino amongst the embryos that hatched, but it never appeared at all healthy, and did not reach maturity.

On the 6th a second brood of seventy-seven appeared; six days later another of sixty-nine. On the 15th forty-seven more; and a fifth brood of only seven appeared to exhaust the capacities of one female. After an interval of five days (on the 21st) there was a fresh oviposition of one hundred and twenty-seven eggs, the first effort of the other female; forty more on the 23rd completed the spawning, making a total of four hundred and seventy-six eggs.

There can be no doubt that three hundred and nine of these eggs can be ascribed to one female, and the balance to the other. These numbers will be seen to be in accordance with the computations of Héron-Royer.

The rapidity with which the embryo develops and breaks through its capsule is striking, two or three of the broods taking only four days to hatch into wriggling larvæ with small four-branched external gills, which disappeared after a few hours.

The gelatinous capsule measured from between 5 and 7 mm.; the vitellus 2·3 mm., dark brown, with large white pale. Length of larva when first hatched, 9 mm.; colour light greyish; tail, well-developed, 5 mm. Length after fifteen days, 15 mm.; tail, 7·5 mm.; light brownish, speckled with darker brown; a darker streak along the vertebral line remaining throughout the larval stage.

After twenty-six days there was only an increase of 2 mm. in the length; the hind legs had just begun to appear as small white stumps.

In thirty-five days they had rapidly reached the length of 25 mm.; and in fifty-four days, after some hot weather, they were 34 mm. long.

Length of body, 16 mm.
Width of body, 10·5 mm.
From tip of snout to eye, 5 mm.
Width between eyes, 4 mm.

Front limbs just visible under the skin; hind limbs with digits well-developed, and transverse lines across femur and tibia. In sixty-nine days the metamorphosis was completed.

This development took place in the garden without any covering or artificial warmth, the tadpoles feeding most voraciously on raw meat.

The first two broods will metamorphose this year, but at the time I write there are many whose development has practically ceased, and will probably not be resumed until the return of spring.