498 BULLETIN OF THE 



yolk of the sperm passage. This marks the termination of the act of 

 fecundation. 



If Calberla's explanation of the reappearance of the " Dottertropfen " 

 is correct, this structure affords a very important index, — easily recog- 

 nized in the living egg, — not only to the time at which the contraction 

 takes place, but also to the energy with which it acts at any given instant. 

 Calberla has further described this process of contraction as an arrange- 

 ment of the yolk granules concentric to the egg nucleus, which makes its 

 appearance at once upon the accomplishment of the nuclear copulation. 

 As the stages of copulation can hardly be said to have been satisfactorily 

 observed, it follows that the most which can be justly claimed is that 

 this stellate arrangement is to be observed about the time of the sup- 

 posed copulation. If Calberla is right in the interpretation of the elon- 

 gated body ^'Spk(V)" indicated in his Fig. 8 as a sperm nucleus, then 

 it is clear the radial arrangement precedes nuclear copulation and has the 

 egg nucleus for its centre, as he himself in one place clearly indicates. 



Even if fertilization does not take place, the egg membrane after a 

 time — twelve hours if the eggs are maintained in cold running water 

 (_|_8° to -|-10° C), sooner if in warmer water — is elevated from the 

 yolk. But whereas in the former case this elevation began around the 

 micropyle and ensued next at the micropyle and only secondarily, as it 

 were, over the rest of the yolk, in the latter case it takes place slowly 

 and uniformly over the whole surface and without definite relation to 

 the micropyle. Moreover, in the latter case neither threads of proto- 

 plasm nor a " Leitband " are formed. Although a " Dottertropfen " ap- 

 pears at the inner micropyle, it is not withdrawn into the yolk and 

 subsequently made to protrude, but ultimately ruptures and is soon 

 followed by the disintegration of the whole yolk. From the moment of 

 the first appearance of the elevation of the egg membrane, even if over 

 only a limited area, the egg becomes incapable of fecundation. How far 

 a possible change in the condition of the superficial clear layer of proto- 

 plasm might interfere with the penetration of spermatozoa conld not be 

 established, as the latter were never seen in these cases to reach the 

 perivitelline space formed by the elevation of the egg membrane. The 

 existence of a " Dottertropfen " in unfertilized eggs Calberla endeavors 

 to explain by assuming that the inflowing water exercises on the yolk a 

 stimulating influence which induces a slight contraction and consequent 

 protrusion of part of the contents of the sperm passage. 



In a short supplement to his paper Calberla compares this "Leitband" 

 with the conical elevation observed by Fol in the case of Asteracanthion, 



