EXPIvANATION OF PI.ATB XX. 



Fig. 49 a-e. The ectoparasite of Nais variabilis, var. punjabensis. 

 ,, 50. Site of approaching fission in Slavina punjabensis, to show distri- 

 bution of pigment. 



,, 51, 52. Two individuals of Slavina punjabensis which have probably 

 recently separated and the anterior ends of which have not 

 yet developed completely. The first nephridium in fig. 52 is in 

 the fifth segment. 



,, 53. Molosoma hemprichi, seen by transparency. Only one set of setae 

 is shown, and the oil-drops in the superficial epithelium are 

 indicated only in the prostomium and at the posterior end. 

 The nephridia are absent from the first and fifth setal inter- 

 spaces. 



,, 54. Head of the same, seen from the side. 



,, 55. Hinder end of the same, showing peri-intestinal sinuses. A few oil- 

 drops are shown near the anus. 



