396 MAINE AGRICULTURAL LXPE^RIM^NT STATION. I912. 



air chamber. The shell consists of several layers of which at 

 least three may be distinguished ; ( i ) the inner or mamillary 

 layer, consisting of minute conical deposits of calcareous mate- 

 rial; (2) the middle spongy layer which is composed of a com- 

 paratively thick mesh work of fibers; (3) a delicate outer shell 

 cuticle. In many eggs there is further deposited in the various 

 shell layers, one or more coats of pigment. 



This brief statement of the more important substances 

 formed by the oviduct serves to show the complexity of the 

 physiological processes which occur within this organ. For 

 some time past, this laboratory has been engaged, among other 

 things, in a study of these physiological processes. To form a 

 basis for further experimental work it has Seemed necessary to 

 gain a more thorough knowledge of the histological structure 

 of the organ with which we are dealing. The present study is 

 thus chiefly morphological. Some discussion of the probable 

 physiological significance of the elements described will be 

 given in the latter part of the paper. In the main, however, 

 these deductions must be supplemented and possibly corrected 

 by later physiological experiments. 



The hen's egg has been a classical object for the study of 

 vertebrate embryology for the past century and a half. One 

 would naturally expect that the formation of the egg itself 

 would have attracted some attention during this long period. 

 It is surprising, therefore, to find so few observations, either 

 on the physiology of the process or on the morphology of the 

 organs concerned. A few of the more important papers on 

 these subjects are mentioned in the following paragraphs. 



The extensive work of Coste ('47 and '49) is one of the 

 earliest studies of these processes. He gives quite accurate 

 and detailed observations on the physiology of the oviduct. He 

 gave us our most complete account of the processes attending 

 ovulation. He also records the observation of an egg in the 

 upper part of the isthmus of which the lower end was covered 

 with membrane while the upper end was naked. He also 

 obsei*ved the formation of the shell. The articles of Merkel v. 

 Hemsbach ('51) and Landois ('65) are chiefly interesting on 

 account of the uniqueness of their views regarding shell forma- 

 tion. They believed that the shell membrane was a direct 

 transformation of the muscular layers of the isthmus. One of 



