336 BULLETIN OF THE 



denied, and appears to be realized especially in the case of unicellular 

 Protozoa. Finally, the endogenous method of cell increase, though much 

 less general than was formerly maintained, is not for that reason to be 

 totally denied. It occurs more especially in the Protozoa and the 

 Mesozoa (Dicyemidse). Common to all forms of increase, save free cell- 

 formation, is a continuity in the successive generations of nuclei. As 

 Von Jhering's review of the palingenetic method of cell increase is simply 

 a fair presentation of what appeared the more salient and unmooted 

 features of the process, with possibly a slight tendency to magnify the 

 observations of Selenka, I shall spare myself the trouble of reviewing his 

 statements in detail. In so far as his paper is a reflection of the ideas 

 prevailing at that time, it warrants me in calling attention to some 

 points at variance with observations on Limax. Von Jhering appears to 

 maintain a direct genetic connection between the radial figure of the 

 spermatic nucleus and one of the two stars which constitute the amphi- 

 aster of the first segmentation sphere."* Although assenting that the 

 asters are not always of the same age, I cannot agree, for reasons else- 

 where expressed, that there is any basis for assuming the implied con- 

 nection. The idea that the systems of yolk rays arise about the ends 

 of the spindle, rather than that the spindle is a diff*erentiation which 

 may make its appearance somewhat later than the asters, is a one-sided 

 view of the possible order of events. It cannot be doubted that the 

 spindle fibres may far exceed the numbers (12-24) given by Von 

 Jhering. It is perhaps premature to say that " the Zellplatte in the 

 case of animal cells is of only theoretical interest " ; at least, traces of 

 the structure in question are so persistent in Limax as to compel the 

 belief that not all of the substance of the interzonal filaments finds its 

 way into the new nuclei. 



In his "Zoologische Studien," Selenka (78, pp. 11 - 14) extends and 

 somewhat modifies his preliminary communication. The incisions at 

 the pole of the segmentation nucleus, at first thought to initiate its 

 fibrous diff'erentiation, are only phenomena of contraction in its welded, 

 but not yet intimately fused parts [pronuclei, Van Beneden], and they 



* " Den auf den Eikern zuwandernden Spermakern hatten wir als das Centrum fiir 

 eine weitgehende Dotterstrahlung kennen gelernt, wahrend dem Eikerne, nachdera 

 er einmal seinen Platz im Centrum des Eies eingenommen, eine solclie nicht mehr 

 zukam. An deni Furchungskerne, kurz nach seiner Entstehung, gewahrt man daber 

 nur ein Centrum der radiaren Dotterstrahlung. Sobald nun der Furchungskern 

 die Spindelform angenommen, erscheint noch eine zweite Sonnenfigur im Dotter, 

 indem jeder Pol der Spindel zum Mittelpunkte eines Strahlensystemes wird. ' 

 (p. 150.) 



