108 J. Thomas Patterson. 



V. Feetilization. 



Since it is intended to describe in detail the process of fertilization, 

 the writer wishes here to make only a brief statement concerning 

 the time of its occurrence. Harper, '04, has shown that fertilization 

 in the pigeon's egg takes place immediately after ovulation, when 

 the egg is in the region of the infundibuliim. The writer finds the 

 same to be true of the hen's egg also. Eggs taken from the upper 

 part of the oviduct at distances varying from one to twelve inches 

 from the infundibulum, give all the stages of development from 

 maturation to the formation of the first cleavage spindle. 



We have shown above that the egg is about twenty-two hours in 

 passing down the oviduct, and since fertilization takes place imme- 

 diately after ovulation, it is obvious that it occurs approximately 

 twenty-two hours before the time of laying. Throughout this paper 

 we shall, therefore, determine the "age" of any particular stage from 

 this estimated time of fertilization. 



VI. The Two-celled Stage, — Three Houes. 



The first cleavage furrow makes its appearance just as the egg 

 is entering the isthmus, about three hours after the estimated time 

 of fertilization, and by the time the inner-shell membrane can be 

 recogiiized as an extremely thin sheet covering the albumin, the fur- 

 row is well developed and covers a distance equal to about one- 

 third the diameter of the area of primary cleavage. The furrow is 

 usually situated in the central part of the disc (Fig. 1). 



Any mention of the first cleavage furrow calls to mind the ques- 

 tion of the relation of the plane of this furrow to the longitudinal axis 

 of the later embryo. Of the five cases so far obtained, in which 

 it was possible to determine absolutely the plane of the first furrow, 

 only one showed it coinciding with the long axis of the future 

 embryo. This would seem to indicate clearly that the plane of the 

 first furrow does not necessarily parallel the median axis of the 

 embryo. It may be, however, that in the case of each of the eggs 

 mentioned, we were dealing with one in which the axis of the 

 later embryo would be abnormal; that is, it would not meet the 

 chalazal axis at right angles. Duval, '84, has pointed out that a 



