1917] Boeck: Mitosis in Oiardia microti 21 



These cysts of Giardia were identified very early by various 

 workers, among them Grassi and Schweiakoff (1888), "Wenyon (1907), 

 Bensen 1908), and Rodenwaldt (1911). Because of the various 

 morphological aspects which these cysts present during different stages 

 in their development, certain stages have received names designating 

 them as definite types of cysts. 



Prior to the appearance of the paper "On Binary and Multiple 

 Fission in Giardia niuris" by Kofoid and Christiansen (1915&), only 

 three tj^pes of cysts were identified. The first type, "single indi- 

 vidual" cysts (pi. 1, fig. 12), was described by the early investigators, 

 Wenyon (1907), Bensen (1908) and others. The second type, or 

 "binary fission" cyst, contained four nuclei, and direct evidence for 

 the cleavage of the body to form two individuals (pi. 1, fig. 16). The 

 cysts containing four nuclei were seen by Wenyon (1907) and Roden- 

 waldt (1911). The third type, the "copulation" cyst, included those 

 in which two individuals were found (pi. 1, fig. 13). These differed 

 from the second type in that the organisms, although separate, 

 appeared to be in a state of partial fusion, suggesting copulation. 

 Schaudinn (1903), in a footnote, refers to Giardia cysts in which he 

 found two individuals adhering to each other by their cytostomal 

 areas, and interpreted this act as one of copulation. It is from this 

 interpretation that this type has received the name of "copulation" 

 cyst. 



It was the prevalent view previous to the paper by Kofoid and 

 Christiansen (1915&) that reproduction in Giardia took place only 

 within the cysts, for no binary or multiple fission of these organisms 

 had been seen in the free state. This paper, representing the results 

 of work on Giardia muris, revealed evidence of the occurrence of 

 binary and multiple fission in both the free and encysted states of 

 Giardia muris. The work of Kofoid and Christiansen also disclosed 

 another type of cyst which may be called the "multinucleate" cyst, 

 for in it were found as many as sixteen nuclei. This type was also 

 found in Giardia microti by the same workers (see Kofoid and Chris- 

 tiansen 1915a). The question was raised by these authors whether 

 certain of these multinucleate cysts with unequal nuclei might repre- 

 sent possible maturation stages or whether the multinucleate condi- 

 tion present was due to "multiple fission of two individuals in the 

 stage of advanced plasmotoray." 



In the light of the evidence upon cysts gathered in my work on 

 G. microti, the four enumerated types of cysts would seem to resolve 



