24 EDWIN LINTON. 



thus forming a solid base on which the yolk rests. Against this 

 base the mass of yolk is hammered by the walls of the ootype. 

 Under this hammering the mass assumes a tetrahedral shape, and 

 during the process the shell is built around it. The material for 

 this shell is secreted by the gland which lies on each side of the 

 common duct between the germarium and the ootype. When 

 the shell is nearly finished, as shown by the cessation of the 

 hammering process of the walls of the ootype, a very small and 

 finely granular mass (Fig. 4, s) makes its appearance suddenly in 

 the common duct at a point (sd') approximately half way between 

 the germarium and the ootype. This cluster of granules, which 

 was in no case seen until it made its appearance in the common 

 duct, travels rapidly along the common duct to the ootype. As 

 soon as it reaches the ootype which now contains the newly 

 encapsuled yolk mass with its associated germ-cell, there is a 

 pause in the movements of the walls of the ootype and common 

 duct for an instant. This pause is followed by powerful con- 

 tractions of the walls of the ootype whereby the egg is forcibly 

 ejected through the uterus (od) into the water. 



The minute granular cluster which was seen entering the com- 

 mon duct immediately before the discharge of an egg, was inter- 

 preted at the time of observation to be spermatozoa, although the 

 duct leading from the seminal receptacle to the common duct 

 could not be seen in the living worm. It can be seen, however, 

 in a stained specimen mounted in balsam and was satisfactorily 

 demonstrated by means of serial sections. 



Both the yolk mass and the spermatozoa appear to be pro- 

 pelled along the common duct by ciliary action. The egg is 

 ejected by powerful muscular action of the walls of the ootype. 



An examination of serial sections showed an interesting feature 

 in the structure of the duct which leads from the germarium to 

 the common duct. It is spacious at its beginning in the gland 

 (/), where it appears in life as a clear space in the center of the 

 germarium in which ripe germs could be seen oscillating when- 

 ever a charge of yolk was passing towards the ootype. The 

 duct grows narrower distally. Indeed the duct (r) is shaped like 

 a funnel. Near the point of union with the yolk duct (<^)it is but 

 little wider than the diameter of a single germ cell. A study of 



