1. Growth in weight of embryonic and larval Ambystoma maculatum from the time that eggs are deposited to the period of metamorphosis may be expressed as a single sigmoid curve. 2. The length curve, except for a short period before hatching when the embryonic axis is curved, is likewise sigmoid. 3. The Ambystoma population of a pond is quite homogeneous, the specimens metamorphosing at approximately the same time. 4. Under natural conditions the relation between weight and length from year to year seems to be constant during the stages before feeding. Later the relationships are variable because of feeding differences. 5. Growth to the time of food ingestion is associated with imbibition of water. Later growth to the time of emergence of the salamanders is correlated with a process in which the percentage of water content decreases. During this period the inorganic constituents gradually increase.