MUSEUM OF COMPARATIVE ZOOLOGY. 249 



Walter's ('58, p. 493, Taf. XIX. Fig. 31. C. 6-8) observations relate to the 

 sperm-cells of Oxyuris ornata, of which he says that, while the cells are 

 growing, a granular mass is gradually deposited around the nucleus, which by 

 aiid by assumes the well-known radial figure peculiar to some Nematodes. 



Clapari:de ('59, pp. 52, 60-63, PI. V. Figs. 16, 17, PI. VII. Figs. 3, 4) con- 

 firmed the observations of Rei chert and Meissner so -far as regards the occiu'- 

 rence of a radial arrangement of the granules in the sperm-producing cells of 

 Ascaris mystax, etc. The nucleus entirely disappears, even beyond the possibility 

 of being recalled by the use of acetic acid. Then the granules, hitherto irregu- 

 larly distributed, move toward the periphery and arrange themselves in rays 

 about a clear non-granular centre. In this stage the cells undergo a prolifera- 

 tion. The nucleus (i. e. the granular mass, which Claparede does not, however, 

 confound with the clear nucleus, now disappeared) divides indifferently into 

 two, three, or four parts. At first there are formed two or three clear spots at 

 the centre of the granular mass ; gradually these separate from each other, and 

 around each of them the granules arrange themselves in rays. Thus are 

 formed several masses with radial structure. The cell suffers constriction 

 around each of these nuclei, and is finally divided into as many daughter 

 cells as there are new nuclei. Claparede is probably wrong in considering 

 these granular masses nuclei, for they must correspond to the asters which be- 

 long properly to the protoplasm surrounding the nucleus. 



In the case of Phallusia mammillata, Kowalevsky ('66", p. 4, Taf. I. Figs. 

 2, 3) has given very clear drawings of optical sections of the cleavage spheres 

 after the first and second segmentations. Concerning the radial phenomena, 

 he says: " Die Dotterkornchen der Furchungskugeln liegen strahlenformig 

 gegen den Kern." 



Leuckart ('67-76, p. 90) also alludes to the same phenomenon when he says 

 of the first segmentation in Ascaris : " Die Dottermoleciile gruppiren sich um 

 die aus einander riickenden Blaschen, wie am ihre Mittelpunkte." 



While KuPFFER ('70, p. 128) corroborates for Ascidia canina the previous ob- 

 servations of Kowalevsky on the radial arrangement of the yolk granules about 

 the nuclei of segmentation spheres, he places emphasis on the fact that it is not 

 peculiar to segmentation spheres, since one finds it as much, if not more, pro- 

 nounced in ovarian eggs after they have become altogether granular ; " es- 

 pecially in the immediate periphery of the germinative vesicle the arrangement 

 of the granules is at times so regular that one fancies he sees a crown of rods. 



Kowalevsky ('71, Taf. IV. Figs. 26, 28, 29) has represented a delicate radial 

 structure in what he considers the nuclei of the cleavage spheres in the case of 

 Euaxes. That Kowalevsky considers this clear radially streaked protoplasm 

 to be the nucleus, is sufficiently evident from his explanation (p. 63) of Fig. 

 26. I think it is quite certain, however, that the radiate structure is no part 

 of the nucleus, but is homologous with the molecular asters of the yolk, as 

 Biitschli ('76, p. 398) has already pointed out. 



The studies of Schneider and other recent observers who have seen astral 

 figures will be considered further on. 



