Experimental Formation of Accessory Organs in Mid Body Lateral-Line of Amphibians. ∗

Abstract

The ability of primary lateral-line organs in amphibians to form accessory ones by budding, 1 , 2 the time at which these bud organs are developed, and the pattern of organ groups gave a method for measuring the effects of the present experiments in amphibians.

When the placodes of the mid-body lateral-line primordia of young and older tail-bud stages of Amblystoma punctatum (Harrison stages 23-24 and 28-29) are exchanged, the age difference between graft and host organ-forming tissue can be clearly followed through the young larval stages by observing the time at which accessory organs are laid down by the budding of primary ones.

In A. punctatum the dorsal and ventral poles of primary organs give rise to accessory organs forming lineal groups of 2 or 3. 1 In A. tigrinum by a similar process groups of from 4 to even 8 are formed, usually in irregular clusters, as in Rana palustris and Hyla crucifer. There is multiple budding of both primary and accessory organs. When the mid-body lateral-line primordia are exchanged in the tail-bud stages of punctatum and tigrinum the formation and grouping of organs from the graft follow only that of the donor species.

When the lateral-line primordium of A. punctatum is placed on the body of A. tigrinum in the future pathway of the primordium of the host, the one of the graft will migrate and form organs only when the primordium of the host touches and fuses with similar material of the graft. The phenomenon is similar to that previously reported. 3 At the appropriate times accessory organs are developed, which in size and group formation are identical with those of the donor species. The organs are innervated by the host lateral-line nerve and never were observed to degenerate up to late larval life.