MUSEUM OF COMPARATIVE ZOOLOGY. 321 



nuclear membrane, whereby the nucleus loses its sharp limitation from 

 the protoplasm ; (2.) a uniform distribution of the nuclear substance 

 through the whole nucleus; (3.) a loss of clearness. This last is attrib- 

 utable to a loss of nuclear fluid during the metamorphosis, which may 

 in the observed cases of Cucullanus and Nephelis amount to one third, 

 or even two thirds, the volume of the unaltered nucleus. What becomes 

 of this fluid (wa^seriger Kernsaft) 1 It is not uniformly appropriated, 

 says Biitschli, by the surrounding protoplasm ; on the contrary, it may 

 be inferred — from the fact that the metamorphosis of the nucleus begins 

 at two points, and that each of the neighboring radial systems of the 

 yolk embraces a clear homogeneous central area, which is at first small, 

 and increases with the metamorphosis of the nucleus — that this fluid 

 escaping at these two points, as Auerbach maintains, becomes accumu- 

 lated in the central areas mentioned. So crude a conception of the origin 

 of the radial figures as Auerbach entertains cannot, he says, be accepted, 

 nor yet can Flpmming be right in considering them due to a structural 

 condition of the protoplasm. First of all, the seat of the cause of the 

 radial phenomenon is to be sought in the central area. The latter, how- 

 ever, does not correspond to the end of the nucleus, and for this reason 

 Strasburger is at fault in referring the cause to an attraction which oper- 

 ates upon the surrounding protoplasm from the ends of the nucleus. For 

 the same reason the area itself cannot be regarded as a mass attracted 

 by the end of the nucleus. What may be the nature of the changes pro- 

 duced in the protoplasm of the area by the nuclear fluid, he is unable to 

 say ; perhaps it is only a simple swelling and solution resulting in the 

 homogeneous and light appearance of the area. 



Aside from Biitschli's failure to see a central structure in the area, it 

 seems to me that the optical properties of the latter — it being more 

 highly refractive than either the surrounding protoplasm or the nuclear 

 fluid — are not easily reconcilable with this interpretation. 



The only deviation from a fusion, sooner or later, of the elements of 

 the nuclear plates, is that observed in the case of the primary nuclei of 

 Infusoria during conjugation. In the case of Paramecia, at least, the 

 plates retain their differentiated condition so that the fibrous, spindle- 

 shaped nucleus divides into two, each of which has a structure like the 

 original. 



Although a trace of a cell plate is to be found in Nephelis and snails, 

 it is unlike that found in plants, for there is no spreading out of the 

 nuclear fibres and the plate does not take part in the formation of the 

 cortical layer (Hautschicht) of the segments. 



VOL. vr. — NO. 12. 21 



