1917] Boeck: Mitosis in Giardia microti 11 



The evidence for the connection of the parabasal bodies with motor 

 activity is mostly morphological in that this organ is found directly 

 upon the axostyle, a unit of the motor apparatus of the free vegetative 

 organism. Often these connections can be demonstrated in the cysts 

 (pi. 1, fig. 12) ; here the connections are very slender fibrils. 



By far the best evidence for the metabolic nature and relationship 

 existing between the parabasal bodies and the organism as a whole is 

 gained from a study of the cysts. It was found that all forms encysting 

 had the parabasal bodies, but that they became very much hyper- 

 trophied (pi. 1, fig. 12). This is explained by the fact that by virtue 

 of encystment all motor activity is slowed down or ceases, and so the 

 draft upon the reserve food-supply in the parabasal bodies decreases 

 or stops and the bodies temporarily enlarge until absorption of food 

 is cut off by the cyst-wall. They then decrease slowly and even disap- 

 pear. This view gains more evidence when it is found that in those 

 cysts in which binary fission of the flagellate had been completed the 

 parabasal bodies were lacking (pi. 1, figs. 13, 16) and also that in the 

 multinucleate cysts these bodies were either very faint (pi. 1, fig. 14) 

 or entirely lacking; in explanation, the bodies had become physically 

 exhausted because of the metabolic activity which must necessarily 

 have taken place in the cyst, while the original source of food-supply 

 had been progressively cut off. 



That these bodies are conveniences to cope with the varying 

 intestinal medium would appear to be established since thus far it 

 has been found that only the entoparasitic organisms have these 

 parabasal bodies well developed. 



MITOSIS 



Mitosis in Giardia microti presents stages characteristic of the pro- 

 phase, metaphase, anaphase and telophase which are in many respects 

 homologous to these phases of mitosis in Metazoa. 



Prophase 



The prophase, in which the chromatin is getting ready for its equal 

 division in the metaphase, is especially marked by the complexity of 

 nuclear changes, most of which occur previous to the division of the 

 centrosomes which is the forerunner and initiator of mitosis in the 

 Metazoa. 



At the time when the first mitotic activity occurs, the division of 

 the blepharoplasts and the beginning of the splitting of the axostyle 



