HISTOLOGY 01^ THD OVIDUCT 0:^* THE DOMESTIC HEN. 425 



oviduct anterior to the vagina, is due the activity of the tubular 

 glands. 



If we extend this idea to the isthmus we may suppose that the 

 membrane is secreted by the tubular glands while the albumen 

 is secreted by the unicellular glands. This is again in accord 

 with the fact that there is an abrupt break in the tubular glands 

 between the albumen portion and the isthmus while the uni- 

 cellular glands are continuous. The abruptness of the break in 

 the tissue layer at this point corresponds very well with the 

 abruptness in the change of function. Just as soon as the egg 

 crosses the line between the albumen region and the isthmus 

 the formation of membrane begins. 



In the albumen region it may be assumed that the tubular 

 glands secrete a very dense albumen while the unicellular glands 

 secrete a more fluid substance which perhaps serves to dilute 

 the former to some extent. There are no observations to sup- 

 port this view but it is not at variance with the facts so far 

 observed. 



In the anterior part of the funnel region only the homologues 

 of the tubular glands are present and here we have a dense 

 membranous substance in the chalazae and their accompanying 

 layer. 



In the vagina only unicellular epithelial glands are found. 

 These differ somewhat in the form of cell and general appear- 

 ance from unicellular glands in other parts of the oviduct. 

 These are perhaps concerned in secreting the delicate outer 

 shell cuticle and the coloring matter of the shell. 



In conclusion it must again be urged that the deductions in 

 the above paragraphs are offered only as suggestions and that 

 sufficient facts either to prove or disprove them are not at hand 



Summary. 



, I. Two muscular layers, an outer longitudinal and an inner 

 circular layer can be distinguished in all parts of the oviduct. 



2. The inner surface of the oviduct is thrown into a num- 

 ber of primary longitudinal ridges. The epithelium over these 

 ridges forms secondary folds. In the uterus the ridges as such 

 are lost and instead there are a number of leaf like folds of the 

 inner surface. 



3. Three types of glands are described: (i) Unicellular 

 epithelial glands occurring between the ciliated cells in all parts 



