224 MICHAEL F. GUYER. 



Aceto-carmine, so frequently recommended for fresh tissues, 

 I found of little value with my material. Its only use was to 

 give information quickly about what stages one might expect to 

 find in his other better fixed material. As one might expect, 

 from the considerable amount of acid in this stain, it quickly 

 swells and distorts chromosomes, and as far as my own prepara- 

 tions were concerned it proved untrustworthy. With the tissue 

 of embryos Bouin's fluid, with and without the addition of 

 chromic acid, was used in the main; sections alone were studied. 



At the outset, in the naivete of my inexperience with photog- 

 raphy under the microscope, I had hoped to present much of 

 my evidence in the form of photomicrography, but although I 

 made many attempts it speedily became evident that the utility 

 of the photographic camera would be decidedly limited. In 

 order to show the objects of sufficient size, high powers had to be 

 resorted to and with them the plane of focus became so restricted 

 that details which were plainly to be seen with very little manipu- 

 lation of the fine adjustment were found to be not at all revealed 

 in the photograph. 



However, even with this handicap, I feel that my photographs 

 reveal convincing evidence of certain features which I wish to 

 discuss, and I have therefore used them for Plates I. and II. 

 Most of the pictures were taken with a Zeiss 2 mm. apochromatic 

 objective and a number 8 compensating ocular. In a few 

 instances a No. 4 or a projection ocular was employed. A num- 

 ber of different brands of photographic plates were tried but 

 the Cramer contrast plates proved to be the most satisfactory. 



GENERAL SCHEME OF SPERMATOGENESIS IN THE FOWL. 



The general histological structure of the testis of the fowl is 

 in the main similar to that of well-known mammalian forms. 

 The chief differences are the more slender character of the 

 seminiferous tubules and the great reduction in the amount of 

 interstitial cells. Thus, the convoluted seminiferous tubules 

 which contain the germinal cells come to make up almost the 

 entire bulk of the testis. 



The walls of the tubules are lined by a layer of spermatogonia. 

 These by growth and division give rise to the various later 



