1918.] T. Southwell & B. Prashad : Parasites of HUm. ^7 



any larval or adult Cestode hitherto described. These differences, as 

 we shall see, are so great and so fundamental as to merit very careful 

 consideration before coming to a conclusion. 



(2) Is the parasite a larval or an adult form ? 



Assuming it to be a larval form the following facts have to be 

 considered : — 



(a) The parasite exhibits, in common with the larval liver-flukes, 

 the peculiar method of parthenogenetic development, but we know of no 

 case among the Trematodes in which such active larval stages are passed 

 in a vertebrate host. Further, nowhere does this type of partheno- 

 genetic development take place within a cyst. Besides this, as the 

 parasite in question has absolutely no trace of a digestive tract, we have 

 no hesitation in concluding that it is not a Trematode larva. 



Turning now to the Cestoda we find that the reproductive process 

 is absolutely unique, whether the parasite be an adult or a larval form. 

 It is unlike any Cestode larva we are acquainted with in being parasitic, 

 absorbing food, reproducing itself, and in the progeny reinfecting the 

 same host. Further, a combination of such adult structural characters 

 as suckers, reproductive organs of whatever kind, and the excretory 

 duct, is not to be seen in any larval Cestode. We are aware of the 

 conditions existing in various species of the genus Piestocystis (3). We 

 have seen Villot's account (6) of this form, as well as Hill's description 

 of his species of Piestocystis hoplocephali and Piestocystis lialis (4). 

 Although our form bears a superficial resemblance to Piestocystis lialis 

 with the head evaginated, in having an unarmed rostellum and 

 four suckers, yet our species, though encysted, has the rostellum and 

 suckers always everted as in adult tape- worms ; this is so even in the 

 young individuals of our species. Moreover, the excretory system in 

 Piestocystis liaUs and other species is open posteriorly, while in the 

 parasite in question it is closed in all stages of its life-history. Also 

 in Piestocystis lialis the buds are produced directly by a proliferation of 

 the internal wall of the cyst. This is a typical larval condition, but in 

 this worm which certainly appears to be an adult, the young are 

 developed by a typical method of parthenogenesis (Lipospermia) in the 

 body of the worm and not form the wall of the cyst. 



For the above reasons w^e have to conclude that the parasite is an 

 adult cestode, though the following facts might be urged against this 

 assumption, viz., (a) Absence of sexual genital organs, both male and 

 female ; (b) the encysted condition of the adult parasite ; but the 

 young parasites, as has been mentioned before, find their way out of the 

 parent cyst, after they have grown to a fair size. They then lie in the 

 mesentery for some time before themselves becoming encysted and 

 repeating the same life-history ; (c) the entire absence of the nervous 

 and water-vascular systems. The absence of these characters, however, 

 in no way interferes wath the acceptance of the form as a Cestode parasite^ 

 which is highly degenerate — a condition which perhaps is to be corre- 

 lated wuth a changed life-history, completed in one host only, as appears 

 to be the case with the form in question. This is further borne out by 

 the extensive infection of the host which results in a very large progeny. 

 (3) If an adult, then is it a primitive or a degenerate form ? 



