MUSEUM OF COMPARATIVE ZOOLOGY. 541 



thickenings. Whereas in the latter case there is a severing of these two 

 constituents of the nucleus, in the former the nuclear substance, still 

 in the form of rods, imbibes nuclear fluid, and the individual rods, 

 swollen into granules, then become confluent, and thus is restored a 

 nuclear mass of uniformly mingled constituents. So far as my observa- 

 tions extend, they do not directly conflict with Hertwig's view^s ; but, 

 theoretically considered, it seems difficult to explain what the signifi- 

 cance of all thi^ metamorphosis may be, if the same fluid constituents of 

 the old nucleus ate to be reabsorbed by the accumulations of readjusted 

 nuclear substance. It appears to me much more reasonable to assume 

 that that which is appropriated by the lateral zones is new substance 

 from the neighboring protoplasm, and even not exclusively the more 

 fluid constituents of the latter. If Hertwig's statements do not imply 

 the reabsorption of the nuclear fluid set free at the disappearance of the 

 membrane of the old nucleus, then I can accept his interpretation ; for 

 he says of a somewhat later stage, to explain the growth, that the nucleus 

 possesses the ability to appropriate from the yolk " fliissige und feste 

 Stoffe." But what may be said of the young nucleus in this respect 

 may also be reasonably ascribed to the nuclear substance existing in the 

 rodlike form. It appears to me certain, from the increase in the total 

 mass of the nuclei with successive segmentations, together with the 

 absence of evidence that the proportion of " nuclear substance " is corre- 

 spondingly diminished, that the nuclear substance of the "thickenings," 

 and afterwards the young nuclei, possess the ability to incorporate w^ith 

 themselves, not only the more fluid constituents from the yolk, which 

 may represent the " Kernsaft," but also less fluid portions, which with 

 equal propriety may be considered " Kernsubstanz." That the central 

 areas of the asters, when such exist, sustain an intermediary relation 

 between the protoplasm on the one hand, and the growing nucleus on 

 the other, can hardly be questioned. It is a significant fact, that the 

 fusion of these zonal rods into a homogeneous body only takes place 

 when the latter have reached, not the apex of the spindle, but the edge 

 of the " area," and are thus in a situation to avail themselves directly 

 of the areal substance. Whether the latter is unaltered protoplasm, 

 or whether it is protoplasmic substance which has already undergone 

 changes rendering it more like that with which it is about to be incor- 

 porated, is not to be answered categorically ; but the signs of chemical 

 activity developing a force which affects the remotest portions of the 

 vitellus are indicative of fundamental changes in the region of these 

 areas, and the properties of their substance which have been observed 



