Abstract
The relative weight of the central nervous system of the frog, Rana pipiens, changes during the active season, and such a change is probably characteristic for other species of frogs with like habits.
The relative weight of the central nervous system is low at the time of emergence, high in the midsummer (July) and low again at the time of hibernation. During hibernation it remains nearly constant. In the formula 1 used to express the weight of the central nervous system, the absolute value of C is characteristic for the station from which the frogs come.
The range from minimum to maximum in the value of C is about 13 per cent., rising 7 per cent. from the end of March to the end of April, 4 per cent. more from the end of April to the end of May, and 2 per cent. more from the end of May to the first of July, remaining stationary in July and then falling month by month at a similar rate to the end of October.
This variation in the relative weight according to season is due to lack of coincidence between the growth of the central nervous system and the growth of the entire body.
In frogs from one to four years old, the body weight more than doubles during each active season, although the precise form of the curve representing this body growth is not known.
The growth of the central nervous system is precocious in relation to that of the body, but in the absence of direct observations on the growth of the body, the form of the curve can only be indirectly determined.
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