158 CRESSAVELL SHEARER. 



this question again, and of determining the manner of formation of 

 these two kinds of ecrgs. 



As Korschelt has determined, the two varieties of eggs are laid 

 together, but they develop immediately without the presence of the 

 male, and are therefore fertilized inside the body of the female. In a 

 few days the small male egg gives rise to the rudimentary male, which 

 at the time it is ready to leave the capsule is full-grown and sexually 

 mature (Fig. 1). The female, on tlie contrary, when she leaves the 

 capsule, is very small, and still in the larval state, the ciHation and 

 arrangement of the segments Ijeing quite different from that in the 

 full-grown condition, which is only attained after a considerable 

 period, and may never be assumed if she does not happen to obtain 

 proper food. Thus in culture jars in which food is not found, the 

 females will remain as long as six months in an immature condition, 

 and never grow up. 



The young worms may be clearly watched within the capsule as 

 segmentation and development proceed. The development is direct, 

 and as the time for hatching approaches, the young larval females are 

 seen to spin round within the capsule. This denotes that they 

 are about to hatch and leave the capsule and commence their free 

 existence. If the capsule is placed under the low power of the 

 microscope at this stage and carefully observed, it will be seen 

 that the little males are actively copulating with the small females 

 at this time within the capsule. The actual transference of 

 the sperm from the testis of the male through the penis into the 

 body of the female can be distinctly seen. Every female as she 

 passes out of the capsule is seen to carry a small mass of sperm, 

 collected under the gut at the junction of stomach and intestine at 

 the point where the ovary will subsequently appear. The rudimentary 

 males seldom or never leave the capsule, dying shortly after the 

 females escape. Examination of any immature free-swimming females, 

 taken from culture dishes at random, always shows that they are 

 all fertilized. If they are carefully fixed and sections cut from 

 them at this stage, it will be seen that the germ cells have not 

 been differentiated, and although a mass of sperm is collected at the 

 point where the ova will subsequently appear, no trace of them 

 can be detected. These only appear at a much later date, when the 

 female has grown considerably in size. They are seen then as a few 

 small refractive cells in the living state, and as small nuclei sur- 

 rounded with hardly any cytoplasm in the stained condition, beneath 

 the gut and amongst the mass of sperm. Shortly after they appear it 

 is seen that each one is joined by a spermatozoon, the head of which 



