Formation of cell masses in the myelencephalon of the clawed frog, Xenopus muelleri
An important process in the organization of developing nervous system is the clustering of neurons with similar properties to form nuclei. The development of myelencephalon of Xenopus muelleri, a pipid frog that retains a lateral line system throughout life, was studied in Nissl stained serial sections. The results showed that density of neurons increases as the animal develops. Cell masses were formed in the latter half of larval stages (stage 48 to 59). Large neurons migrate first before small neurons. Raphes and reticular formation nuclei and Mauthner cells were the earliest neurons that could be distinctly recognized on the ventral part of the myelencephalon. By stage 54 out of 66 stages, the structure of the myelencephalon resembled that of the adult frogs.