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the cysts of Prowazekellci lacertae. For a similar reason I regarded the I-cysts 
as being probably vegetable organisms, but they are now known to be cysts 
of lodamoeba williamsi. I had also noted (1910) that degenerating Cliilo- 
mastix mesnili could assume appearances closely resembling blastocystis. 
Swellengrebel’s (1917) conclusion is that blastocystis ‘‘is not the name of a 
zoological genus but of a peculiar form of degeneration to which representa¬ 
tives of different genera of intestinal protozoa may be liable.” On the other 
hand future investigations may show that blastocystis is derived from amoebae 
and it must be admitted that the large binucleate cysts of Entamoeba coli 
with the large vacuole occupying almost the entire cyst bears some resem¬ 
blance to binucleate forms of “blastocystis.” Frequently in stained prepara¬ 
tions containing small entamoebae, such as Endolimax nana, and blastocystis, 
it is possible to trace what might be regarded as a complete series of connecting 
links between a typical amoeba and a typical blastocystis and one is constantly 
tempted to adopt the view that, the series traceable is a real one. Macfie (1915) 
regarded certain blastocystis associated with an entamoeba in the monkey 
Cercopithecus petaurista as cysts of the entamoeba. His proof of this, however, 
appears to be wanting and furthermore we know that the entamoebae of the 
monkey produce the typical entamoebic cysts with four or eight nuclei. 
Alexeieff (1911) says that at one time he regarded the blastocystis of the 
lizard as derived from the lizard flagellate but that later observations have 
altered his opinion and that he has come to look upon blastocystis as a purely 
vegetable organism. He was largely influenced in this by the character of the 
development of a yeast ( Schizosaccharomyces octosporus), and has suggested 
the name Blastocystis enterocola for the intestinal blastocystis. 
Dobell (1908) in criticizing Prowazek’s work on the autogamy cysts of 
Bodo compares them with very similar cysts he had seen in the gut of the frog 
and which he proved by germination to be of a vegetable nature. It appears 
to me that Prowazek’s cysts, though not autogamy cysts as he describes them, 
are at any rate true cysts of the flagellate. At least this can be stated of some 
of those he figures. 
It is evident therefore that there is a difference of opinion as to the true 
nature of blastocystis and we must await further information. It seems pos¬ 
sible that under the name blastocystis three distinct structures have been 
confused: the true protozoal cysts like those of the lizard flagellates, vegetable 
organisms like the cysts Dobell studied in the frog or which Alexeieff saw in 
the case of his yeast Schizosaccharomyces octosp.orus, and thirdly, degenerate 
intestinal protozoa or even tissue cells, some of those in the human intestine 
belonging to the second group and others to the third. 
Trichomonas lacertae Prowazek, and Trichomastix lacertae Biitschli. 
I have nothing to add to the description of these two organisms as given 
by Prowazek (1904). I have seen none of the conjugation forms described by 
him.. The flagellates are shown in PI. XX, Fig. 2, h and i. 
Parasitology xn 
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