Representative individuals at relevant developmental stages. Tadpoles were photographed alongside a mm ruler and labelled with Gosner  stage. We also divided stages 20 to 21 into substages based on level of eye transparency . Stages were defined by the following criteria. 19: no blood circulation in the gills; 20: blood circulation in the gills and minimal corneal transparency (not shown); 20.25: corneal transparency extending 1/4 way down eye (not shown); 20.5: corneal transparency extending 1/2 way down eye; 20.75:corneal transparency extending 3/4 way down eye; 21: cornea fully transparent (not shown), 22: tailfin transparent and circulation observed.