On the basis of dry wt., regions of the gastrula differ in their respiratory activity. There are 2 respiratory gradients: an animal-vegetal gradient and a dorso-ventral gradient. With respect to total N, there are also 2 respiratory gradients, just as found on the basis of dry wt. However, when total N is used as reference standard the animal-vegetal gradient is steeper than that based on dry wt. Since total N can be considered as a measure of protein, there are also 2 respiratory gradients on the basis of protein. There is a respiratory vegetal-animal gradient when rates are expressed in terms of dipeptidase activity. If it is assumed that hyaloplasm has a uniform chemical composition, dipeptidase activity is a measurement of the amt. of hyaloplasm. It follows that when hyaloplasm is used as a reference standard there is a vegetal-animal respiratory gradient in the gastrula. The nearer the vegetal pole, the higher is the respiratory activity per unit amt. of hyaloplasm. When the extractable fraction is used as reference standard, there is no difference in respiratory activity between regions. The extractable fraction is essentially a measurement of "non-yolk" protoplasm. Therefore, when non-yolk protoplasm is employed as a basis, the regions of the gastrula respire approx. at the same rate. However, the extractable fraction is found to be a heterogeneous material. An intrinsic positive correlation is found, at least between the dorsal lip and the ventral lip, in their respiratory activity. When the dorsal lip respires at a higher rate, the ventral lip also consumes O2 at a higher rate.