THE DEVELOPMENT OF BEHAVIOUR IN ELEUTHERODACTYLUS MARTINICENSIS (AMPHIBIA, ANURA)

In the genus Eleutherodactylus , development is wholly embryonic. Among other features of ontogeny which are thereby modified is the development of behaviour. Within the egg envelope, the embryo is largely still, but wriggles from time to time. These movements represent all that remains of the axial swimming behaviour of larval Amphibia. The embryo develops normally when removed from the envelopes, and its reactions to light touch can then be studied from day to day. In E. martinicensis , which develops from first cleavage to hatching in 13-14 days, the first movement of the legs is seen during trunk wriggles at 7 1/2 days, but a day later they can move independently. The first reaction of the leg is a slow withdrawal; at 9 1/2 days flexion is followed by a vigorous extension. By then, reflexes affecting all four limbs can be elicited.
Towards the end of embryonic life, limb movements can be maintained in continuous cycles, and the animal can then swim. When it is allowed normally to emerge from the envolopes, the juvenile toad, smaller than a house fly, can jump a distance of over a foot. These observations are discussed in relation to the ontogeny of behaviour in other vertebrates, particularly in regard to the views of G. E. Coghill.