214 FEKTILIZATIOX OF THE OVUM 



would thus seem to lie of the same nature as the disapj^earance of 

 the sperm-centrosomes, and both Boveri's theory of fertilization and 

 the general hypothesis of the ])ormanence of the centrosomes would 

 receive a serious blow. 



The investisjators to whom these observations are due have rani^ed 

 themselves in two groups in the interpretation of the phenomena. 

 On the one hand, Lillie and Child do not hesitate to maintain that 

 the centrosomes actually go out of existence as such, to be re-formed 

 like the asters out of the egg-substance ; and that such a new forma- 

 tion of centrosomes is possible seems to be conclusively shown by the 

 experiments of Morgan and Loeb described at pages 215 and 307. On 

 the other hand, Sobotta, MacFarland, Kostanecki, and Coe, relying 

 partly on the analogy of other forms, partly on the occasional pres- 

 ence of the centrosomes during the critical stage, urge that the dis- 

 ajipearance of the sperm-centrosomes is only apparent, and is due to 

 the disappearance of the asters, which renders difficult or impossible 

 the identification of the centrosomes among the other protoplasmic 

 granules of the egg. These authors accordingly still uphold Boveri's 

 theory. 



It is difficult to sift the evidence at present, for it has now become 

 very important to reexamine, in the light of these facts, those cases 

 in which the absolute continuity of the centrosome has been main- 

 tained — for example, in Ascaris, Chcetoptcnis, and Thalassema — in 

 order to determine whether there may not be here also a brief critical 

 period in which the centrosomes disappear. There are, however, 

 some facts which tend to sustain the conclusion that even though the 

 sperm-centrosomes disappear from view, there is some kind of genetic 

 continuity between them and the cleavage-centrosomes. First, both 

 Kostanecki and Wierzejski ('96) and Coe ('98) have found that there 

 is some variation in eggs apparently equally well preserved, a few 

 individuals showing the sperm-centrosomes at the poles of the united 

 nuclei at the same period when they are invisible in other individuals. 

 Second, both these obsen'ers, Coe most clearly, have shown that the 

 egg-centrosomes disappear considerably earlier than the sperm-cen- 

 trosomes, and Coe has traced the sperm-centrosomes continuously to 

 the exact points {the poles of the iDiited nuclei) at which the cleavage- 

 centrosomes afterivard appear {Y\^. 155). This important observation 

 leads to the suspicion that the apparent disappearance of the centro- 

 somes may be due to a loss of staining-capacity at the critical period, 

 or that even though the formed centrosome disappears its substance 

 reappears in its successor. Here again we come to the view sug- 

 gested at page 1 1 1, that the centrosome may be regarded as the vehicle 

 of a specific chemical substance which is transported to the nuclear 

 poles by its division, and may there persist even though the body of the 



