478 BULLETIN OF THE 



origin from the cortical layer (Hautschicht) of the yolk. This he now 

 corrects, and says the error was due to the " Eikern " lying in this case 

 (Phallusia) so near to the surface.* After new observations he accepts 

 the views of Hertwig in holding that the '" segmentation nucleus" arises 

 from the fusion of two nuclear structures. The sperm nucleus, which is 

 smaller than the egg nucleus, makes its appearance, according to Stras- 

 burger, in IJ^ or 2 hours after artificial fertilization, close to the outside 

 of the "Eikern" between the latter and the Hautschicht, op. cif., Taf. 

 VIIL Fig, 4. It is at once surrounded with homogeneous protoplasm, 

 which is" continuous on its peripheral side with the " Hautschicht," and 

 causes here a slight elevation of the surface. Rays emerge from this 

 homogeneous protoplasm, but around the egg nucleus there are none. 

 In another hardened egg (Taf. VIII. Fig. 5) he finds a larger single nu- 

 clear structure surrounded with rays, and concludes that it results from 

 the fusion of the germ- with the egg-nucleus. He does not, however, 

 agree with Hertwig, that the egg nucleus is the germinal dot, and from 

 a review of the studies of others on animal eggs concludes " dass es sich 

 auch in den Fallen der Erhaltung des Eikernes nicht um diesen Kern 

 als morphologisches Element, sondern nur um dessen Substanz handle " 

 (pp. 311, 312). An entirely parallel view is held touching the method 

 of the formation of the sperm nucleus. In the case of Phallusia it is 

 quite possible that the substance of the spermatozoa " diffundirt " 

 through the egg membrane, and re-collects within the yolk to form a 

 sperm-nucleus. In fecundation, then, it is probably a question of the 

 introduction of nuclear substance into the egg, yet only as a physiological 

 element, not of the introduction of the nucleus of a spermatazobn as a 

 morphological element. 



" With the greatest care to prevent fertilization," Greeff {"7Q") has 

 raised the larvse of Asteracanthion rubens. The only difference between 

 the development of fecundated and unfecundated eggs consists in the 

 tardiness with which segmentation takes place in the latter case, — it 

 being ten to twelve hours after exclusion, instead of one to two hours, as 

 in fecundated eggs. 



In his account of the development of Heteropoda, Fol ('76, pp. 113, 

 144) says that what remains of the star after the emergence of the polar 

 globule again approaches the centre of the vitellus and becomes rounded 

 into the form of a nucleus ; near the opposite or nutritive pole a second 

 nucleus appears, which also moves toward the centre. These nuclei em- 



* I have elsewhere (pp. 420, 421 ) shown how probable it is that Strasburger has 

 in some cases confused another structure with the "Eikern." 



