No. I.] THE EGG OF UMAX AGRESTIS. 213 



been formed by the penetration of the spermatozoon. In the 

 fertilization of the eggs of some of the mollusks, notably in 

 Arion ^ and in Physa,^ the tail follows the head of the spermato- 

 zoon into the ovum. When the tail is present in eggs, it is 

 generally easily recognized by its strong affinity for certain 

 stains, a characteristic which may be acquired after its entrance 

 into the o.^^, according to Van Beneden and Platner. I have 

 never seen any evidence that the tail of the spermatozoon 

 enters the ^^^ of Limax, but the difficulty of obtaining eggs 

 at the time of the earliest contact of the spermatozoon with 

 the ovum makes it impossible to determine whether the tail- 

 piece has really penetrated the tgg and there broken down, or 

 whether it has been left outside. 



I have never been able to detect a middle-piece in the sper- 

 matozoon after it has entered the 0.%,%, or to recognize a rotation 

 of the sperm-head. Very little change occurs in the sperm-head 

 from the time it first enters the egg until the eggs are deposited, 

 although when the eggs are laid the sperm has probably been 

 in the Q.g^ for some hours. All eggs taken from the oviduct 

 and from the albuminous gland were found in individuals that 

 were dissected in the late hours of the evening — from 8 to 

 10 o'clock P.M. As eggs are rarely deposited during the night, 

 before the early morning hours, it seems probable that at least 

 several hours must elapse between the time of fertilization and 

 the depositing of the eggs. 



While the archiamphiaster occupies the middle of the ^^%, 

 the sperm-head remains quiescent at the periphery, very near 

 its place of entrance at the lower pole. Sometimes the sperm- 

 head is oblong, and sometimes it is slightly constricted in the 

 middle in the form of a dumb-bell, as in PI. XI, Fig. 4. It is 

 homogeneous, however, and always stains uniformly. As the 

 spindle moves toward the upper pole of the ^z^, preparatory to 

 the formation of the first polar body, the sperm-head loses its 



1 Platner, " Ueber die Befruchtung von Arion empiricorum." Archiv f. mikr. 

 Anat., Bd. xxvii, 1887. 



2 Kostanecki und Wierzejski, " Ueber das Verhalten der sogenannten achroma- 

 tischen Substanz im befruchteten Ei : Nach Beobachtungen an Physa fontinalis." 

 Archiv f. mikr, Anat., Bd. xlvii, 1896, 



