Developmental Changes in Primary Lateral-Line Organs Studied in Living Larvae of Anurans and Urodeles

Abstract

In amphibian embryos the migrating lateral-line primordia lay down a series of primary organs which can be observed in the living and vital-stained condition.^{1, 2} Since the mid body line extends down the tail in rather transparent tissue such organs are favorable for study in the living specimen when observed under high magnification in micro-aquaria. These data concerning the developmental changes in primary tail organs of normal larvae provide a basis for further observations consequent to the cutting of the lateral-line nerve.

In Amblystoma punctatum larvae the large melanophores often obscure the view of many lateral-line organs and their nerves. This condition was easily avoided by feeding specimens an exclusive diet of enchytraea which, for some unknown reason, contracts the dark pigment cells. The animals become pale yellow in color. In Hyla crucifer tadpoles pigment presents no serious difficulties. In contrast to the normal pigmented larvae of Rana palustris it was found that hypophysectomized specimens gave as clear a picture as Hyla.

In Amblystoma punctatum the tail organs begin abruptly at a level above the anus. In many larvae studied at the feeding stage (Harrison stage 46, 15-16 mm.) such a line on the tail is about 18 in number, extremes being 13 to 20. As in other lines the number on the right side is usually not equal to that on the left.

From primary organs accessory ones are formed by budding from supporting cells.^{1, 2} Shortly after the feeding stage begins the terminal organ may give off a bud posteriorly and thus form a chain of 1 to 3 new organs. However, normal isolated animals often do not show an immediate response by budding of the terminal organ until later.