SENSE ORGANS 



121 



The length, weight or age of the animals used are not given 

 the significance of the measurements therefore lies in the 

 relations which are shown, rather than in the absolute values, 

 though these probably apply to a full grown animal. 



Ear. Gray ('07) gives the measurements on the mature 

 cochlea as in table 81. 



Wada 0'23) has made an elaborate study of the growth of the 

 cochlea at nine ages from birth to middle life. A summary of 

 the fundamental measurements is given in table 82. In this 

 summary the tables referred to are those in the original Memoir. 



Wada found one rat in a litter of five which responded to 

 auditory stimuli at nine days. The tunnel of Corti in this rat 

 was open, while in the non-hearing litter mate, it was closed. 

 The cell bodies in the ganglion spirale were still much below 

 the size which they finally attain see table 82. 



TABLE 83 

 Area of skin in albino rat Hill and Hill ('13) 



8. Integument. Myers ('21) reports as follows: 



The deposit of the subcutaneous fat is most marked in the neighbor- 

 hood of the milk ducts formed and prospective. From birth to ten 

 weeks of age, the subcutaneous fat is distributed in the same manner 

 in both male and female rats. We believe the deposit serves as a pro- 

 tection against cold and as a reserve food supply. The absence in the 

 rat of a uniformly distributed layer of protective fat may be related to 

 the early development of hair and to the habit of living in closed spaces. 

 In rats underfed from birth, the deposit of subcutaneous fat becomes 

 scanty, and the development of the milk ducts is retarded. 



The absolute area of the skin has been nieasured in square 

 centimeters by Hill and Hill ('13) in five rats. The values are 

 given in table 83. 



