242 ERNEST E. JUST. 



point to the first cleavage plane? I here, therefore, give only 

 as much of an outline of its formation and of the development of 

 the egg to the time of first cleavage as will suffice to render 

 intelligible the subsequent record of observations. 



Almost at the moment the spermatozoon touches the egg 

 membrane, the contents of the cortical layer begin to flow out 

 as a viscid transparent substance of the same refractive index 

 as water, leaving only radiating lines across the space (perivitel- 

 line space) between protoplasm and membrane which represent 

 the walls of the emptied alveoli. This jelly in its flow carries 

 the ink from the periphery of the egg so that between each egg 

 and the surrounding ink is a clear space. This outflow of jelly 

 may last for fifteen minutes. The jelly forms about the egg a 

 layer everywhere continuous except along the tail of the sperm 

 which thus forms a canal that increases in length as the jelly 

 area widens. 



Below the spermatozoon, the protoplasm of the egg begins to 

 form a cone at thirteen to fifteen minutes after insemination 

 which gradually increases in height until it reaches the membrane 

 and then slowly retrogresses. With this retrogression, the mem- 

 brane at this point sinks; in this depression lies the sperm. 

 During this behavior, as the jelly area widens, the canal in the 

 jelly in which the tail of the sperm lies fills in with particles of 

 ink. This process is a gradual one, the indicator reaching its 

 maximum of development fifteen to twenty minutes after in- 

 semination. The indicator, therefore, is formed along the tail 

 of the sperm and points to the entrance-point of the sperm. 



Twenty minutes after insemination, the spermatozoon may be 

 seen attached to the membrane at the end of the indicator. The 

 perivitelline space now becomes slight. The egg "assumes an 

 amoeboid appearance" (Wilson), changing its shape and becoming 

 very irregular. The sperm cannot be seen readily (Fig. 5). 

 About forty minutes after insemination the egg becomes spherical 

 again. The sperm is easily visible on the membrane which is 

 more widely separated from the protoplasm by the perivitelline 

 space. 



This condition is of short duration for the egg begins another 

 series of changes. The membrane appears everywhere equi- 



