EARLY DEVELOPMENT OF THE PIGEON'S EGG. 233 



easily seen in the paraffin cake for orientation in cutting. Klein- 

 enberg's picro-sulphuric acid (strong solution) plus 10 per cent, 

 acetic has been the most successful for killing and fixing, al- 

 though other solutions have been used. 



Fertilization. 



Dr. Harper (3) found that the egg is fertilized in the evening, 

 at the time it leaves the ovarian capsule and enters the oviduct 

 and he makes this statement, " In all cases observed, this has 

 taken place between seven and nine o'clock." I shall, therefore, 

 refer to eight o'clock in the evening as the hour of fertilization, 

 although the exact time for any particular oviducal egg is not 

 known. 



To present the history of the early development, I shall de- 

 scribe several critical stages as follows : 



1. Position of the supernumerary sperms at the close of 

 maturation. 



2. The 8-cell stage. 



3. The 16-cell stage. 



4. The last stage of the multiplication of the sperm nuclei. 



5. The disappearance of the sperm nuclei. 



6. The periblast. 



7. The growth of the blastodisc at the expense of the periblast. 



8. The germ wall. 



1. Position of the Supernumerary Sperm Nuclei at the Close of 

 Maturation. — In an egg taken from the oviduct at 1 1:30 P. M., 

 or about three and one half hours after fertilization, the first 

 cleavage plane had not formed. In this egg, the supernumerary 

 nuclei had migrated into the periblast at the periphery of the 

 germinal area, and they occupied a circle which in later stages is 

 indicated superficially by accessory cleavage. Some of these 

 nuclei were in mitotic division. 



2. The 8-cell Stage. — Abundant material has been obtained 

 in stages of two and four cells, but for brevity, a description of 

 those stages is omitted from this paper. 



At 4:45 A. M., eight and three fourths hours after fertilization, 

 an egg of eight (or perhaps nine) cells was taken from the shell 

 gland. Its surface view is shown in Fig. 2, and a transverse 



