Changes in Numbers and Dimensions of Glomeruli During Metamorphosis of Pelobates syriacus (Anura; Pelobatidae)

Changes in glomerular numbers and volume were followed throughout five ontogenetic stages of Pelobates syriacus (Anura, Pelobatidae). The number of glomeruli increased markedly between the 2-legged and the 4-legged tadpole stages. In the post-metamorphic stages the number of glomeruli was about twice their number during the tadpole stages. Glomerular volume peaked during the 2-legged tadpole stage, when the tadpole reached its maximal size, and dropped thereafter. There is some evidence to indicate that the number of glomeruli in post-metamorphic P. syriacus increased during growth thus indicating perhaps an increase in their functional importance. The number was still lower than that reported for some other anurans, more similar to the numbers given for representative urodeles, however, the latter have considerably larger glomeruli. Two main factors appear to be involved in regulating numbers and volume of glomeruli in frogs. The ontogenetic changes during metamorphosis affect both glomerular numbers and volume, whereas post-metamorphic growth affected only the glomerular numbers.