In a previous paper (Cleland, 1950b) some aspects of the intermediary metabolism of the unfertilized oyster egg were detailed. A study of the enzymatic architecture of the cell seemed desirable since this knowledge is necessary for a clear formulation of the problems of cell division and differentiation in relation to metabolism (Cleland, 1950a) and would relate the metabolism of the egg to a previous study of cell architecture (Cleland, 1947). Such a study was made in the 1949 and 1950 seasons and forms the basis of this paper.In Tecent years cell respiration has been shown to be intimately connected ^rith cell granules. While mitochondria were very early linked with cell metabolism (cf. Cowdry, 1918) a specific connection with respiration was first suggested by Kingsbury (1912) and Mayer et al. (1914). Although Warburg (1914) demonstrated that much of the oxidative activity of sea urchin egg brei was associated with the granular components, the relevance of the finding to the mitochondrial problem was not appreciated and this type of study lapsed. The mitochondria respiration relation was supported by Joyet Lavergne (1927-38) but none of this work can be considered conclusive.Studies of centrifugally-broken Arbacia eggs provided a number of suggestive facts. The experiments of Shapiro (1935) indicated that the heavy halves, which contain the pigment granules and about three-quarters of the yolk granules, havo a higher endogenous respiration than the light halves, and Ballentine (1940) from his study of the distribution of reducing systems considered that they were associated with the granules. These studies were not extended to quarter eggs in which granule fractionation is more satisfactory. Hutchens et al. (1942) made a study of the distribution of cytochrome oxidase in various fractions separated from sea urchin egg homogenates. They were led to conclude that a considerable fraction was present in the ground cytoplasm where it was also most active in terms of total N. This finding is diflScult to reconcile with that of Navez and Harvey (1935) and with more recent reports.Mitochondria were first separated from cells, and analysed, by Bensley and Hoerr (1934) but seven years elapsed before their respiratory characteristics were examined by Lazarow (1943), Lazarow and Barron (1941). Chantrenne (1944) showed that cytochrome oxidase and succinoxidase are present in the granules separated from yeast and other cells. Schneider (]946a) and Hogeboom et al. (1946) demonstrated the presence of succinoxidase and cytochrome oxidase on the mitochondrial fraction. The presence of the tricarboxylic acid cycle and fatty acid oxidase in mitochondria was demonstrated by Kennedy and Lehninger (1949).Most of the recent work has been done on mitochondria from mammalian liver and little attention has been paid to the general validity of the distribution. However, Recknagel (1950) has shown that cytochrome oxidase is associated with the mitochondrial fraction of the frog's egg, the large yolk granules having little activity, ...