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ONE TEXT F1QUR.E AND TEN CHARTSStudies on the weight of the entire brain of the albino rat at different ages and at different body weights and in the wild Norway rat at different body weights have been already published (Donaldson, '08, '09, '18 ; Donaldson and Hatai, '11). As a continuation of these studies it was desired to determine also the growth relations of the parts of the brain and thus to extend the corresponding observations by Hatai ('XI), Sugita ('17), and Stewart ('18). For this purpose studies have been made on the brains of 250 male and 213 female albino rats and, for comparison, on the brains of 53 male and 71 female wild Norway rats.The collection of the material extended over several years, but as all the dissections were made by the same hands, the irregularity arising from the technique is minimized. Similar material has been collected from inbred, exercised, and gonadectomized rats, as well as from those used for other tests, but the present report deals only with data from the normal stock Albinos and from the series of wild Norways just mentioned.

TWELVE CHARTSComplete quantitative data on the various anatomical components of the body are important not only for the study of growth, but also for cross reference. A lack of such reference data interferes in many cases with a clear recognition of alterations which are taking place in the animal body under various experimental conditions. Fortunately the following data on the growth of the albino rat are already available:Growth of body in weight in respect t o age (Donaldson '06) and body length (Donaldson '09) ; weight of the brain and spinal cord (Donaldson '08) ; weight of total amount of blood and hemoglobin content (Chisolm 'll), the growth of the head, trunk, extremities, skin, skeleton, musculature and viscera in weight according to age (Jackson and Lowrey '12); and finally the growth of the dry substance in the albino rat (Lowrey '13). Besides these we have several other series of data on the albino rat, though not so comprehensive as those just cited.

The object of the present paper is to report on the condition of several of the internal organs of the albino rat after castration, spaying or semi-spaying. These series of spayed and semi-spayed animals were prepared by Dr. Stotsenburg and have been used by him for studying the growth of the body in weight as affected by the respective operations (Stotsenburg '13). The castration of the animals here used was also performed by Dr. Stotsenburg but in this series the growth of the body was not followed, the effect of this operation having been previously determined (Stotsenburg '09).I wish t o acknowledge the courtesy of Dr. Stotsenburg in allowing me to make the postmortem examinations in all of these interesting cases.All the necessary details concerning the operations and the care of the animals have been already given by Stotsenburg ('09, '13) but two points should be mentioned here as these are important for the interpretation of the results: (1) in all instances the operation was performed on young rats about a month old and (2) in the cases of castration the testes with epididymis were removed.Regarding the method of examination of the various organs, as well as the significance of the various formulas used in determining the calculated values from the observed values, the reader is referred to a paper published recently by myself (Hatai, '13). 297