237 



side of the midliue have been so shifted by the stresses of cell division 

 as to lie unmistakably on the opposite side". Kopsch has likewise 

 emphasized the significance of this fact: "Auf die Bedeutung dieser 

 Verschiebungen für unsere Frage haben 0. Hertwig sowie Jordan 

 und Eycleshymer aufmerksam gemacht und sie gegen Roux' Ansicht 

 verwertet. Um so mehr muß es Verwunderung erregen, daß 0. Schultze 

 diesen Punkt gar nicht erwähnt hat und seiner Bedeutung nicht gerecht 

 wird Was wird nun bei solchen Verschiebungen aus der ur- 

 sprünglich vielleicht planen ersten Furchungsebene? Es entsteht eine 

 zerknitterte, gebogene, gewundene Platte, deren Richtung gar keine 

 Beziehung mehr zur Symmetrieebene hat." 



In Figs. 41 — 46 are shown six stages in the cleavage of a single living 

 egg. If the course of the first cleavage groove be followed from the 

 stage represented in Fig, 41 to that shown in Fig. 46, it will be seen 

 that as a result of cell displacement it becomes more and more irre- 

 gular. In this particular egg the displacement of cells is less marked 

 than usual. The second cleavage planes have formed in such a manner 

 that they appear continuous but are in reality two separate cleavage 

 grooves. Each of these shows such a marked shifting that its iden- 

 tification in Fig. 46 would be impossible had it not been kept under 

 continuous observation. A glance at Figs. 34, 35, 39, 40, will show 

 that more striking displacements frequently occur. 



A detailed description of the shifting of the various grooves is not 

 given since the Figures 21—46 give a more perfect conception of 

 these changes than could be obtained from any description however 

 extended. 



If the course of the first or any subsequent cleavage groove be 

 followed from the time of its formation until it becomes lost in the 

 labyrinth of grooves, it will be noticed that at each successive cleavage 

 it becomes more and more tortuous. If this same process be con- 

 tinued until the embryo appears — and there is every reason to believe 

 that it does — we should eventually find that it becomes so irregular 

 that it is impossible for the median plane of the embryo to coincide 

 with it. 



Evidence from Puncture Experiments. 

 The writer has elsewhere (Anat. Anz., Bd. 22, 1902) figured and 

 described the results of a series of puncture experiments on the egg 

 of Necturus and pointed out the bearing of these experiments on the 

 problems in mind. It was shown that the exovates diagonally placed 

 on opposite sides of both the first and second cleavage grooves, were 



