460 L. V. DOMM AND MARY JUHN. 



when unilateral castration was performed on birds aged seven 

 months. The surviving testis was retained about a year. 

 Benoit concludes that there is a hypertrophy of the surviving 

 gonad when the one member of the pair is removed in very 

 young birds; unilateral castration of older birds, after the testes 

 have achieved approximately their normal size is not followed 

 by a compensatory increase in the weight of the surviving 

 gonad. 



The results published by Benoit agree on the whole with those 

 obtained in this laboratory, but we differ slightly from him in 

 the observations on older birds as will appear in the discussion. 



The phrase "compensatory hypertrophy" defines the con- 

 ception, viz: that loss results in stimulating the growth of the 

 surviving member to an extent that tends to restore a normal 

 quantitative balance between the total gonad tissue and the bird. 

 It involves the corollary that there is a normal quotient for 

 weight of bird divided by weight of gonad tissue. The present 

 study aims merely at testing this assumption. The difficulties 

 arise from the fact that the assumed normal quotient of weight 

 of bird divided by weight of gonad varies (i) with age very 

 markedly; (2) with the time of year, age being the same; and 

 that (3) no organ of the body probably is so susceptible to 

 general conditions of health as the testis. These difficulties 

 create numerous sources of error for any very exact formulation, 

 so that we felt that it was not desirable in the present status of 

 this subject with reference to our main problems to use a suf- 

 ficient amount of material and time to reach quantitative 

 results. The present study, although it gives positive results, is 

 therefore merely suggestive. 



It is a pleasure to express our thanks to Professor F. R. Lillie 

 for his continued interest in the work and for his helpful sugges- 

 tions during its course. 



II. DATA ON UNILATERAL CASTRATION. 



All the unilateral castrations were carried out on pure bred 

 Brown Leghorn cockerels that were obtained from one well-known 

 source. The birds were divided into four groups, the first being 

 about one week of age, the second sixteen weeks, the third 



