no J. Thomas Patterson. 



this egg they showed signs of preparation for the next division when 

 they had reached a distance from the membrane equal to 0.175 mm. 

 Polyspei^my. A close study of surface views of two-celled stages 

 has failed to reveal any trace of the "accessory cleavage," which is 

 such a characteristic morphological feature of the early pigeon blasto- 

 derm. It would be a great mistake, however, to conclude from this 

 that fertilization in the hen's egg was monospermic, for a study of 

 the sections brings to light the fact that ordinarily five or six super- 

 numerary sperm nuclei are in the egg, and, as we shall see later, 

 some of these may migrate to the periphery of the area of primary 

 cleavage and there give rise to a rudimentary accessory cleavage. 



In one egg (Fig. 5), which is in a j^recleavage stage of develop- 

 ment, twenty-four extra sperm nuclei are fouud. This high number 

 is very unusual, and led the writer at first to assume that the egg 

 was abnormal. All the evidence, however, is against this assump- 

 tion. In the first place, it can not be said that the physiological 

 condition of the egg was such as to favor the multiplication of the 

 sperm nuclei soon after their entrance into the egg; for if this were 

 the case there ought to be evidences of nuclear multiplication, but 

 not a single sperm nucleus gave any sign of undergoing division. 

 .In the second place, the egg in all probability was normal in so far 

 as undergoing normal development is concerned, for the cleavage 

 nucleus was in the act of producing a spindle at the time when the 

 egg was fixed, and other eggs from this hen underwent normal devel- 

 opment when incubated. 



In the light of these facts it seems evident that in some few eggs 

 a comparatively large number of sperms may enter. In such eggs 

 this may be due to a greater attraction between the protoplasm of 

 the disc and that of the sperms than ordinarily exists; or to a 

 failure of the inhibitory agencies to become operative quickly enough 

 after ovulation to prevent their entrance. 



In the egg from which Fig. 1 was made only five supernumerary 

 sperm nuclei are present, and none of these had reached the margin 

 of the disc at the time when the egg was fixed, but all are located cen- 

 trally. Two of the nuclei are situated quite superficially in the disc, 

 while three have passed down deep and are resting on the coarse 

 granular yolk (Fig. 9). One of the nuclei has undergone division 



