Histolytic Influence of Atrophying Gills During Metamorphosis

Abstract

Helff 1 has shown that the perforations in the opercular integument are the end result of an orderly process of cellular histolysis, due to the histolytic action of the atrophying gills. The present investigation was designed to determine the stage of gill atrophy at which this histolytic influence is most effective.

Homoplastic transplants of gills in various stages of atrophy were made to regions beneath the back skin of metamorphosing Rana pipiens tadpoles. The following constitute the main stages of gill atrophy investigated: (1) a stage showing the earliest macroscopic signs of atrophy; (2) a stage just prior to the release of the fore-limb; (3) a much later stage in which the integuments of the opercular region and the fore-limb had fused, following the release of the latter. Other atrophying gill transplants were made of stages intermediary to these, but the differences in the histolytic action were more clear cut when comparing the transplantation results of the 3 stages mentioned above.

Typical perforations were formed in the skin of the back directly in contact with the gill transplants. Histological sections of integument bounding such perforations showed that histolysis had taken place, identical to normal opercular integumentary histolysis. The stage of greatest histolytic influence of the atrophying gill was determined by the length of time necessary for the transplant to form a uniform sized perforation in the integument. This stage was found to be that just prior to the breaking through of the fore-limb. At this stage the gills are of a reddish hue, quite mushy in consistency, and capable of producing a perforation within 2 days.

The results indicate that the histolytic influence of the atrophying gills is cumulative. It is very weak during the early stages of gill atrophy, but increases proportionately with increasing atrophy and reaches a maximum just prior to the release of the fore-limbs. Following the release of the fore-limbs the histolytic influence of the gills still persists, but gradually subsides as the gills undergo their final stages of atrophy.