362 
Protozoa of Lizards, etc. 
elongate or even dumb-bell shaped. The growth of the cyst is remarkable but 
a similar growth takes place during the development of the oocyst of the 
malarial parasite in the stomach of the mosquito. It is evident that the cysts 
are not very resistant bodies, but that they are destined to pass out of the 
body is supported by their occurrence in greatest number at the hinder end 
of the intestine. 
The fully formed cyst contains comparatively little cytoplasm, which is 
grouped around the nuclei on the inner surface of the cyst wall. The bulk of 
the cyst contains liquid, through which strands of a coarse network of more 
refractile material run and which connect with the nuclear areas. Even 
though not possessed of very tough or impermeable walls it is possible 
that these cysts would take a considerable time to dry completely on account 
of their enormous fluid content. The development of the cyst beyond the 32 
nuclear stage I have not been able to follow but Prowazek (1904) and later 
Chatton (1917) have seen these large cysts give rise to numbers of flagellates. 
The description I have given depends entirely on stained films as prolonged 
observations on the living cysts were not made. That two individuals encyst 
together seems undoubted but if one wished to be hypercritical one could 
suppose that the two associated individuals either before or after encystment 
were the results of division and do not represent conjugation. My interpre¬ 
tation of the appearances seems the more probable one and is in conformity 
with Chatton’s own observations. It must, however, be admitted that an 
absolute proof of the process has not been obtained by me. Further observa¬ 
tions on this parasite might yield some interesting facts in connection with 
the conjugation process of flagellates and the origin of the parabasal bodies 
and centrosome. 
Blcistocystis . 
As already pointed out, many of these flagellate cysts bear a striking re¬ 
semblance to blastocystis and as a matter of fact I have been accustomed to 
regard them as such. In the lizards I have examined, all the so-called blasto¬ 
cystis have the very characteristic nucleus with the surrounding parabasal 
bodies, so there can be no doubt that they are stages in the development of 
the flagellate cysts. Whether side by side with the true flagellate cysts there 
exists a “ Blastocystis of vegetable nature I cannot say at present, but it 
cannot be doubted that ProwazeJcella lacertae encysts in the gut of the lizard 
and that the cysts have been frequently styled “blastocystis.” 
What then is the blastocystis which occurs so commonly in the human 
intestine and that of other animals? Prowazek (1911) maintained that they 
were cysts of Trichomonas but there is no evidence to support this view. 
Swellengrebel (1917) has suggested that they are degenerate forms of various 
intestinal protozoa, while Jepps and Dobell (1918) have noted that certain 
degenerate forms of Dientamoeba fragilis resemble dead blastocystis. I my¬ 
self have, for want of evidence to the contrary, always regarded them as of 
a vegetable nature and this may be the case in spite of the resemblance to 
