1917] Boeck: Mitosis in Giardia microti 9 



expresses no theory as to the functions of these bodies, but believed 

 their presence to be a criterion for determining the age of the flagel- 

 lates. He says that the bodies are present in old forms and not in 

 young forms. This conclusion, however, is unwarranted from the 

 study of G. muris (Kofoid and Christiansen, 1915&) and from my 

 study of G. microti, for both small and large forms may be found 

 without this organ. 



In another group of organisms, the trichomonad flagellates, the 

 parabasal rod is correlated with the well-developed undulating mem- 

 brane (Kofoid and Swezy, 1915). They found that "in the absence 

 of such a localized area the parabasal body or homologue is often more 

 condensed (not however in trypanosomes) and lies nearer the blepharo- 

 plast and nucleus, as in Para joe nia." Their final conclusions, how- 

 ever, are that its function is "not primarily skeletal, or supporting, 

 but rather connected with the metabolism of, and possibly also with 

 the control of, the motor activity. ' ' 



With regard to the function of the parabasal bodies in Giardia 

 microti an hypothesis may be made based on the evidence revealed in 

 the study of both the vegetative and encysted forms. From this study 

 I am led to believe that these parabasal bodies are conveniences on the 

 part of the flagellate for coping with the intestinal medium in which 

 it lives; that they are connected with the motor activity and in rela- 

 tion to the metabolism of the flagellate. 



Most vegetative forms have this organ well developed, but occa- 

 sionally some will lack it and they may be either large or small forms 

 (pi. 1, fig. 10) ; some forms show the organ to be small in size (pi. 1, 

 figs. 4, 11). There are three explanations for these differences: First, 

 an investigation of the parabasals during encj'stment reveals the evi- 

 dence that at the end of encystment the bodies are very faint (pi. 1, fig. 

 14) or entirely absent (pi. 1, figs. 13, 16), so that when plasmotomy 

 occurs the daughter individuals would lack this organ (pi. 1, fig. 13) ; 

 this would explain the absence of this organ in small forms which 

 recently have been the products of plasmotomy and have not had as 

 yet sufficient time for the organization of these bodies. Secondly, the 

 organ may be fading out due to exhaustion from excessive activity on 

 the part of the host — either motor or mitotic activity in some cases 

 (pi. 1, figs. 10, 11) ; this may be true in large individuals which may 

 not show evidence of mitosis. Thirdly, its absence may be due to the 

 non-absorption of the stain, due to the biochemical state the bodies 

 were in at the time of the preparation of the material. 



