The Progress of Ossification in the Skull of the Cricketfrog Pseudacris nigrita triseriata

THE need for morphological studies dealing with the larval stages of the Amphibia was pointed out by Orton (1946). Much of the literature relating to the subject of this present report, the ossification of the skull during the larval period of an anuran, is included in the review of de Beer (1937). Probably the most important is the paper of Erdmann (1933) reporting his observations on Triton and Rana. More recently Lynn (1942) described ossification in Eleutherodactylus nubicola, an anuran which has no tadpole stage. The description given here is the result of detailed observations of 23 specimens of the three-lined cricketfrog, Pseudacris nigrita triseriata. This particular species was chosen because of the availability of its eggs in large numbers, its relatively short larval period, and its small size, all being factors which made collecting eggs and rearing the larvae in the laboratory more convenient. The specimens used comprise a series covering three of larval growth beginning with the time of emergence of the forelimbs or stage XX of Taylor and Kollross (1946). Expressions such as at 5 days or at 3 weeks 211