THE EMBEYONIC DEVELOPMENT OF THE OVAEY AND 

 TESTIS OF THE MAMMALS. 



BY 



BENNET MILLS ALLEN. 



From the Hull Zoological Laboratory, University of Chicago. 

 With 7 Plates and 5 Text Figures. 



This work was carried on with the aim of solving the following prob- 

 lems: (1) The origin and development of the seminiferous tubules and 

 their homologues in the ovary; (2) the origin, development and homo- 

 logies of the rete tubules together with their relations to the Mal- 

 pighian corpuscles of the mesonephros on the one hand, and to the 

 seminiferous tubules of the testis on the other; (3) the origin, devel- 

 opment and homologies of the connective tissue elements and inter- 

 stitial cells of the ovary and testis. 



Incidental to the solution of these problems, the work has involved 

 to a greater, or less extent a consideration of the following allied prob- 

 lems: (1) The development of sex cells; (2) the morphological phases 

 of sex differentiation; (3) cell degeneration in the sex gland and rete; 

 (4) the degeneration of the mesonephros and the development of the 

 Wolffian and Miillerian ducts. 



This work, covering as it does a very broad field, naturally touches 

 upon many points that have already been treated by previous workers. 

 Although much has been written upon this subject there is a singular 

 lack of unanimity in the results attained. This is largely due to the 

 fact that only in a very few cases has the process of development of 

 the sex gland been followed in an extensive series of stages. Su6h work 

 has naturally resulted in giving rise to many false and contradictory 

 views upon these subjects. 



The difficulties in the investigation of these problems are further 

 enhanced by the fact that the sex glands are composed entirely of meso- 

 dermal tissue, in which a large part of the cells are without definite 

 cell boundaries. 



2. Material and Technique. 



The material employed includes numerous stages in the develop- 

 ment of the ovary and testis of the rabbit, from the 13-day embryo 

 to and including adult stages. The pig material includes only em- 

 bryonic stages, but is more complete for the period covered than is 

 the rabbit material. 



American Journal of Anatomy. — Vol. III. 

 8 



