MUSEUM OF COMPARATIVE ZOOLOGY. 289 



Flemming finds that in Anodonta (Taf. III. Fig. 2), after the egg begins 

 to elongate, previous to constriction, a disklike body, which stains deeply 

 in carmine, occupies the middle of the clear figure connecting the two 

 suns, and that a less intensely stained small spherical body occupies the 

 centre of each sun. The latter he is inclined to think are the begin- 

 nings of the new nuclei, thus agreeing with Fol as to the place where the 

 nuclei arise. 



I believe the disklike body is almost unquestionably the nuclear plate, 

 and not, as Biitschli (76, p. 248) thinks, the cell plate. 



The two radial figures, which are visible some time before the first 

 segmentation, and which are of unequal size, (proportionate, namely, to 

 the size of the two cleavage spheres that are about to be formed,) are no 

 longer to be seen when the elongation preparatory to cleavage begins. 

 Flemming is inclined to interpret (p. 128) the existence of single cells 

 containing, as previously reported by himself, two nuclei, to be a pa- 

 thological phenomenon, although stating as a possible explanation that 

 it may not be of so much importance, after all, whether the new nucleus 

 arises a little sooner (before division), or a little later (after cleavage). 



In Lacinularia the only noticeable difference from Anodonta is to be 

 found (p. 183) in the fact that the centres of the radial systems are not 

 such distinctly limited clear spots as in the egg of the latter. 



The primary (Keim) as well as later segmentation spheres divide while 

 in the cytode condition (p. 184). 



His ('75, pp. 35 - 39) contributes no new observations touching the 

 question. Whence arise the parablastic cells ? although he urges grounds 

 against considering them derivatives from the cells of the germ layer. 

 Indirectly, therefore, he implies that they arise de novo in the cortical 

 layer of the yolk (Rindenschicht) and that their nuclei have not arisen 

 by a process of division. 



Soon after his last-mentioned paper, Bijtschli published ('75") fur- 

 ther observations on the nucleus and its metamorphoses during cell 

 division. The investigation of the contents of the testes in the case of 

 Blatta resulted in showing that the nuclei of the multinuclear germ cells 

 of spermatozoa did not undergo such a fusion as he had observed in the 

 cases just reviewed, and as he expected, to find here. The phenomena 

 accompanying the division of the germ cells were, however, a striking 

 repetition of the changes traced in his previous paper. In one point 

 only does the author find reason to change his views. He now concludes 

 that the spindle-shaped body results from the metamorphosis of the 

 whole nucleus, not simply of the nucleolus. The nucleus suffers a con- 



VOL. VI.— NO. 12. 19 



