SEGMENTATION. 233 



protoplasm of the nucleus into that of the cell 1 . The appear- 

 ance of striation may on this hypothesis be explained as due 

 to the presence of granules in the protoplasm. When the 

 streaming out of the protoplasm of a nucleus into that of a cell 

 takes place, any large granule which cannot be moved by the 

 stream will leave behind it a slack area where there is no move- 

 ment of the fluid. Any granules which are carried into this 

 area will remain there, and by the continuation of a process 

 of this kind a row of granules may be formed, and a series of 

 such rows would produce an appearance of striation. In many 

 cases, e.g. Anodon, vide Flemming*, even the larger yolk- 

 spherules are arranged in this fashion. 



On the supposition that the striation of these figures is 

 due to the outflow from the nucleus, the appearances presented 

 in Elasmobranchs admit of the following explanation. 



The central body consisting of two cones (figs. 7 a, 7 c] is 

 almost without question the remnant of the primitive nucleus. 

 This is shewn by its occupying the same position as the primitive 

 nucleus, staining in the same way, and by there being a series 

 of insensible gradations between it and a typical nucleus. The 

 contents must be supposed to be streaming out from the two 

 apices of the cones, as appears from the striae in the body con- 

 verging on each side towards the apex, and then diverging 

 again from it. In my specimens the yolk-spherules are not 

 arranged with any reference to the radiating striation. 



It is very likely that in the cases of the disappearance of the 

 nucleus, its protoplasm streams out in two directions, towards 

 the two parts of the cell which will eventually become separated 

 from each other ; and probably, after the division, the matter of 

 the old nucleus is again collected to form two fresh nuclei. 



In some cases of cell-division a remnant of the old nucleus is 

 stated to be visible after the fresh nuclei have appeared. These 

 cases, of which I have not seen full accounts, are perhaps 

 analogous to what occasionally happens with the germinal 



though, as far as they go, quite in accordance with those of Strasburger, do not supply 

 any grounds for deciding on the meaning of these stride ; and in some respects they 

 support Strasburger's views against those of other observers, since they demonstrate 

 that in Elasmobranchs the modified nucleus does actually divide. 



1 This is the view which has been taken by Auerbach (Organologische Studien). 



* Loc. cit. 



B. 1 6 



