The Early Development of the Pigeon's Egg. 33 



Harper found eight chromatin vesicles in what he supposed were 

 sperm nuclei in a late cleavage stage. But they were periblast 

 nuclei, and the number of vesicles is not significant. See Figs, 14 

 and 14a. Riickert finds merocytes among the cells of the germ 

 layers, and admits that it is impossible to distinguish their nuclei 

 from others whose origin is the cleavage nucleus. But if the mero- 

 syte nuclei of the selachian are derived from the marginal blasto- 

 meres, they naturally do resemble other nuclei in the germ layers. 

 If the reptiles and selachians would breed in confinement, so that 

 the approximate time of fertilization could be determined, and if 

 a close series of stages could be obtained from them as has been 

 done from the pigeon, the material would probably demonstrate 

 the early disappearance of the supernumerary sperm nuclei and 

 the subsequent organization of a periblast homologous with that 

 already described for the teleost (Agassiz and Whitman, '84,) and 

 for the bird (Blount, '07). The homology of the periblast with the 

 vegetative pole of the holoblastic vertebrate eggs will be discussed 

 in another part of this paj^er (p. 49). 



Function of the Supernumerary Sperms. — There still remains 

 the question of the function of the supernumerary sperm nuclei. 

 Bonnevie suggested that they provide the somatic chromatin and 

 that they are offered for "die harmonische Weiterentwickelung des 

 befruchteten Eies." But the variation in the number of spermatozoa 

 does not support this suggestion. In the pigeon. Harper found from 

 12 to 25 supernumerary sperms. Elickert found in fertilization 

 stages among nineteen areas of Pristiurus from 7 to 47, and in 

 twenty germ areas of Torpedo in the same stages from 1 to 56 

 supernumerary nuclei. In the stage of the first cleavage nucleus 

 of the adder, Ballowitz found in nine germ areas a variation from 

 8 to 36 supernumerary nuclei. In one-fifth of all cases, Oppel 

 could not prove the presence of merocyte nuclei. Henking found 

 forty-seven monospermic and forty-eight polyspermic eggs of one of 

 the hemiptera. If one supernumerary spermatozoon is enough to 

 restore the nucleoplasmar balance in the egg of Torpedo, fifty-six 

 are too many. If half of the eggs of one of the hemiptera develop 

 after the entrance of only one spermatozoon, more than one is not 



