I<S MAINi: AGRICUIvTURAIv EXPERIMENT STATION. I9IO. 



The walling in of the ovary in all directions except the one 

 occupied by the mouth of the oviduct in the manner described 

 must tend to decrease the chance of yolks getting free in the 

 body cavity. Even with this arrangement such an accident 

 sometimes happens. In autopsies of a large number of laying 

 hens in a few cases yolks have been found among the viscera. 

 1 umors which appeared to be formed around such yolks have 

 also occasionally been found. It is not possible with our pres- 

 ent knowledge to draw conclusions as to the extent of this 

 apparent structural adaptation among birds. Even in the spe- 

 cies where the air sacs have been carefully studied, the descrip- 

 tion of their attachments and position in relation to the viscera 

 have not been given in detail. From such descriptions as exist 

 it appears that the left abdominal air sac does not uniformly 

 isolate the genital organs so completely as is here described for 

 the domestic fowl. 



Owen* states that "the air receptacles of the thoracic-abdom- 

 inal cavity present varieties in their relative sizes and modes 

 of attachment in different birds" (meaning different species). 

 Muller ** states that in the pigeon the walls of the abdominal 

 air sacs are almost entirely free. Baerf has demonstrated that 

 the abdominal air sacs are absent in the cassowary. Data are 

 wanting as to whether the oblique abdominal septum of Butler 

 occurs in these cases. It is possible that this septum occurs 

 throughout the class Aves even when the abdominal air sacs 

 bear other relations than those described in the domestic fowl, 

 or even when they are absent. 



The general result of this section of the paper is to show, 

 with detailed anatomical description of the relations involved, 

 that there is formed in the hen a sort of "pocket" in which the 

 ovary lies. This "pocket" is of such a nature that, quite apart 

 from any physiological activity on the part of the funnel of the 

 oviduct, the ova separated from the ovary at ovulation are 

 mechanically directed towards the funnel mouth. 



* Owen, R. On the -Anatomy of Vertebrates. Vol. II. Birds and 

 Mammals. London (Longmans) 1866. 



** Muller, B. The Air Sacs of the Pigeon. Smithsonian Misc. Col. 

 Quarterly Issue, Vol. 50, Part 3, No. 1724, pp. 365-414. 



t Baer, M. Beitrage zur Kenntnis der Anatomic und Physiologic der 

 Atemwcrkzeuge bei den Vogeln. Ztschr. wiss. Zool. Bd. 61. 



