MUSEUM OF COMPAEATIVE ZOOLOGY. 279 



From this it appears prebable that Schneider observed the metamor- 

 phosis of the nucleus quite as accurately as either of the three remain- 

 ing observers, but failed to discover that the radiation in the protoplasm 

 was from two separate centres rather than from a continuous line.* 



FoL has observed (73, pp. 474-476, Taf. XXIV. Figs. 2, 11) that in 

 the fresh-laid, fecundated eggs of Geryonia the nucleus is unlike the ger- 

 minative vesicle of the unfecundated eggs. It appears like a vacuole on 

 account of the refractive power of its substance being less than that of 

 the surrounding protoplasm. It is possible to distinguish a membrane 

 (eigene Wandungen) around this vacuole only after treatment with 

 acetic acid, and then with little distinctness. From this, and its size, 

 Fol concludes it cannot be identified with the germinative vesicle of the 

 unfecundated egg, which contains a vesicular germinative dot, but he re- 

 tains for it, nevertheless, the designation of " germinative vesicle." Just 

 before the first segmentation this germinative vesicle [primary cleavage 

 nucleus], has a more confused look and undergoes many changes of form. 



the much more conspicuous groups of '* cords." The middle one of these three bands 

 falls in the plane of cell division, and apparently corresponds to the cell plate of 

 Strasburger. 



The figures presented by Schneider recall even more forcibly than the text the 

 similarity already alluded to, which exists between his observations and those of 

 riemming on certain tissue cells. Another point is the discovery, in the formation 

 of spermatozoa, of cells "in der Viertheilung " (p. 117 and Fig. 8. ^), presenting con- 

 ditions parallel to those pointed out by Russow and Strasburger for pollen cells. 



The opinion expressed above, that Schneider failed to recognize the radial struc- 

 ture as centring in two points, is possibly not quite just, for he says (p. 114, l. c): 

 "Die polare Anordnung der Kornchen findet man bekanntlich auch beim Furchungs- 

 process der Ascidien und Seeigel." Schneider {l. c, p. 138) calls attention in the 

 explanations of figures to the fact that the polar arrangement of the granules is insuf- 

 ficiently brought out in Fig. 5. b. Finally, this metamorphosis, which most likely 

 occurs in those cases where the nucleus appears to vanish, is not the only method of 

 cell division. Two methods must be recognized : one in which the nucleus under- 

 goes the indicated metamorphosis ; the other in which the nucleus retains its form 

 (p. 115). 



* P. S. — Compare this description with the pinnate arrangement of the astral 

 figures recently described by Fol ('79, p. 167) for Toxopneustes. 



Fol seems to have remained for some time ignorant of the discoveries of Schneider, 

 as he makes, I believe, no mention of the latter's work except in the paper last cited, 

 and there (l. c, p. 207) states that he knows of Schneider's work only through 

 Biitschli's citation. Since Fol appears to be in doubt as to whether Schneider's paper 

 was published in the same year as his own paper on Geryonia, or the year following, 

 it seems to be but a matter of justice to emphasize the fact that Schneider's paper was 

 published in April, 1873, therefore about seven months before the paper in which Fol 

 recorded his observations in the case of Geryonia. 



