238 BULLETIN OF THE 



The changes affecting this clear spot are briefly as follows (pp. 116- 

 118). The spot, which at first appears quite round from whichever side 

 viewed, becomes lengthened in the direction of a diameter, and assumes 

 successively the forms of a biscuit (Semmel) and of a figure 8, and finally 

 becomes fully separated (i. e. differentiated) from the remaining yolk- 

 mass.* This process is one of segmentation or division. The constricted 

 " spot " migrates toward a definite point of the periphery. The end 

 which the contents of the spot approach, becomes considerably en- 

 larged, so that the clear spot assumes the form of a blunt rounded 

 cone.f If the egg of Lymnaeus vulgaris arrived at this stage be 

 crushed, it will be found that the spot really consists of two globular 

 parts surrounded by a transparent protoplasmic substance (Schleim) 

 ■which considerably increases the size of the spot. The very thin enve- 

 lope (Halle) of the spheres contains a transparent albuminous fluid, 

 of the same nature as the surrounding protoplasm (Schleim). In the 

 case of Limax agrestis the phenomena are substantially the same. The 

 two spheres become readily distinguishable, especially when one of them 

 moves outward (through the yolk).$ 



* " Der Anfangs vollkommen runde Fleck verlangert sich in der Richtung des einen 

 Durchmessers, nimmt durauf eine biscuitanhliche Form an, dann die Form einer 8 

 und zuletzt trennt er sich ganz von der iibrigen Dottermasse. " 



Another rendering of this passage would be, "and finally becomes completely 

 eliminated from, the remaining yolk-mass." There is also one other passage which 

 might possibly support this view. I shall presently quote and endeavor to 

 explain the second passage. The objection to accepting any interpretation which 

 admits that the spot is eliminated, is the positive denial of it subsequently made 

 by Warneck. 



t " Das Ende, welchem sich der Inhalt des Fleckes nahert, vergrossert sich 

 bedeutend, so dass der helle Fleck die Gestalt eines stumpfen, abgerundeten Kegels 

 annimmt." 



I As the passage last alluded to (Warneck, '50, p. 118) seems to have been the 

 cause of some misunderstanding, I will give it in full: " Es bilden sich also im 

 hellen Flecke bei Limax auch zwei Kugeln, welche besonders deutlich unterschieden 

 werden konnen, wenn die eine von den Kugeln nach aussen tritt, wie es gleich 

 beschrieben werden wird." 



The interpretation of the author's statement turns on the meaning of "nach aus- 

 sen tritt." I understand by it the same as would have been expressed by say- 

 ing " nach aussen — nach der Peripherie zu — tritt." Had it been the intention of 

 the author to say that one of the spheres was eliminated, he would have used 

 "heraustreten." 



The difficulty of understanding what is meant results from the addition of the 

 clause, "wie es gleich beschrieben werden wird." There is nothing in the subse- 

 quent description to which this allusion can refer, except the formation of two polar 

 globules. It is probably on account of this that "Warneck has been understood to 



ii 



