436 HOLMES. [Vol. XVI. 



Asplanchna, points to the conclusion that the egg possesses 

 a certain degree of cytoplasmic organization, which tends to 

 determine the cleavage in a certain direction, even in opposi- 

 tion to Hert wig's law. And this naturally leads one to suspect 

 that the first cleavage plane may be predetermined in eggs like 

 those of most mollusks and annelids in which no means of 

 orienting it are apparent. 



The observations of Blochmann ('82) on Neritina show, if 

 correct, that in this form it is very probable that the longitu- 

 dinal axis of the embryo is determined before the first division. 

 Blochmann found that in the two-cell stage the granules which 

 later go into the tip cells of the lateral arms of the cross were 

 aggregated into two small patches on the two sides of the ^gg. 

 If these groups of granules existed, as seems very probable, 

 before the first cleavage, it would show that the axial relations 

 of the embryo were determined in the undivided Q.gg. " Aus 

 dem Umstand," says Blochmann, " dass die hellen Kornchen 

 schon auf dem Stadium der Zweitheilung vorhanden sind (Fig. 

 39), kann man wohl folgern, dass die beiden Anhaufungen auch 

 schon in dem eben in die Furchung eingehenden Ei vorhanden 

 waren, und dass sie die Enden eines Durchmessers einnahmen, 

 also eine Achse bestimmten." And Blochmann adds, in a foot- 

 note : " Bei unbefruchteten Eiern habe ich manchmal nach dem 

 Austritt der Richtungsblaschen um den animalen Pol eine An- 

 haufung von solchen hellen Kornchen beobachten konnen (Fig. 

 23 bis 26), wage jedoch vor der Hand nicht zu entscheiden, ob 

 dieselben hierher zu beziehen sind." It is unfortunate that 

 Blochmann's observations on this latter point were not more 

 decisive. Could the chief axes of the ovum be determined 

 before fertilization, it would manifestly exclude the possibility 

 that the entrance path of the spermatozoon determines the 

 longitudinal axis of the future embryo. If in any eggs with 

 determinate spiral cleavage the direction of the first cleavage 

 plane and, consequently, the median axis of the future embryo 

 is determined only after fertilization, as is claimed by Mead in 

 the case of Chaetopterus, it may still be true that the spiral 

 character of the first cleavages is determined by a bilateral 

 organization of the ^gg substance, which is developed between 



