xiii, b, 5 Haughwout: Flagellated and Ciliated Protozoa 235 



The author (Hadley) points out the obvious difficulty of escape 

 from the hosts that these parasites buried deep in the tissues 

 would meet; but again we may find instances of this very con- 

 tingency in the literature on the Protozoa, where the death of 

 the host is necessary before the spores can be disseminated. 

 However, he shows how the parasites may return to the lumen 

 of the caecum by spreading downward and inward through the 

 cores of the villi, finally breaking through the epithelium by 

 sheer pressure of numbers, much as they made their entrance. 



Kofoid and Swezy, (26) in their studies of mitosis and multiple 

 fission in the trichomonads, bring out several points that are of 

 interest in connection with the work of Kadley. They state their 

 inability to present conclusive evidence "that either leads ,to 

 gamete formation by maturation divisions, or that either follows 

 zygote formation or fertilization." This knowledge they believe 

 will come only with the solution of the history of the "true 

 trichomonad cysts." 



There is a great diversity of opinion as to whether the encysted 

 stage of Trichomonas or some other flagellate is represented 

 by Blastocystis. Wenyon, (50) while admitting that on occasions 

 it has seemed to him that degenerating Trichomonas or Tetrami- 

 tus may become centrally vacuolated and resemble Blastocystis, 

 thinks it is untenable to view the latter as encysted Trichomonas. 

 Kofoid and Swezy are skeptical of the relation of Blastocystis 

 to Trichomonas and figure Trichomonas with an engulfed cyst of 

 Blastocystis enterocola. However, that does not necessarily 

 constitute a conclusive argument, for I have seen Vahlkampfia 

 engulf cysts of its own species. Galli-Valerio(i5) found double- 

 contoured cysts in the feeces of guinea pigs infected with Tricho- 

 monas, after the faeces had been kept in a damp chamber for 

 one month. When warmed, the cysts opened and discharged 

 small flagellates. Administration of the cysts caused infections 

 in other animals. Alexeieff(i) and Brumpt(4) doubt encyst- 

 ment in Trichomonas and state their belief that these cysts 

 (Blastocystis) represent a stage in the life cycle of some fungoid 

 or yeast organism. 



Swellengrebel {; has reviewed the entire controversy and, fol- 

 lowing an investigation, reaches these conclusions: 



1. In two cases Blastocystis was found where the presence of Tricho- 

 monas or Chilomastix could be excluded with absolute certainty. Con- 

 sequently Blastocystis cannot be a normal developmental form of either. 



2. In fresh stools Blastocystis is but seldom found to be alive and even 



'Parasit. (1917), 9, 451. 



