FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 



Immediately on insemination, sperm pierce the jelly hull, 

 reaching the vitellus with rapid spiral movements; the moment 

 the tip of the sperm touches the cortex of the vitellus all move- 

 ments cease, the head and tail in a straight 

 line at right angles to a tangent of the egg 

 surface. Penetration follows as an activity 

 of the egg; the spermatozoon does not bore 

 its way in the egg pulls it in. 2 After the 

 head has disappeared within the cortex, mem- 

 brane elevation begins. 



After the sperm head has completely dis- 

 appeared within the egg, the cortex reacts 

 to penetration by pushing out a blister at 

 the site of sperm entry (Fig. 2). This blister, which is not 

 optically empty but contains minute drops that wander across 

 this newly formed perivitelline space, may push off at once to a 



..- 



FIG. i. 1 Freshly shed 

 egg. Its pigmented 

 jelly is as yet un- 

 swollen by the sea 

 water. 



3 4 



FIG. 2. An egg ten seconds after the disappearance of the sperm head within 

 the egg. 



FIG. 3. Same as Fig. 2. 



FIG. 4. Four seconds after the membrane began lifting. Free vesicles beneath 

 the membrane. 



distance equal to the greatest the membrane ever reaches (Fig. 

 2); or, what is more common, the membrane elevation slowly 

 sweeps (Figs. 3, 4, 5, 6, 7, 8) around the surface of the egg in- 

 creasing the width of the perivitelline space after having lifted 

 off from the egg at all points (F''g. 9). One may picture the 

 process thus: By escape of substances from the cortex at the 



1 Figs, i, 9, 10, and n were drawn with the aid of a camera lucida. All others 

 are of necessity free-hand sketches. Except in Fig. i, the jelly hull is omitted, x 

 marks the site of sperm entry. 



2 Kupffer and Benecke in 1878 made similar observations on the lamprey egg 

 and reached the conclusion that the sperm Is engulfed. 



