1922] Kofoid-Swczy : Mitosis and Fission in Giardia enterica 205 



The contractility of the eytostome is suggested by its variable out- 

 line in fixed material (cf. pi. 23, figs. 3, 4, 5), and by the vaiying ratios 

 of the anteroposterior and transver.se diameters. The postmargin is 

 more deeply indented in the contracted state than in the uncontracted, 

 and the anteroposterior diameter is 0.80 of the transverse in the con- 

 tracted to 0.82 in uncontracted. In other words, the anteroposterior 

 grip of the eytostome is greater than the transverse. 



There is no evidence of any other function of the eytostome than 

 that of an organ of adhesion. No gullet leads from it and no food 

 particles can be found in the cytoplasm. We have not succeeded in 

 cultivating Giardia in physiological salt solution, in culture media 

 such as peptone broth, or in human ascitic fluid or diluted blood, in 

 most of which the human intestinal flagellates {Chiloniastix, Tricho- 

 monas) live for some time if frequently transferred to fresh media. 



The fact that Giardia enterica has a powerful organ of attachment 

 in the eytostome affords an anatomical ground for the persistence with 

 which infection is maintained in the bowel of man when exposed to 

 the pressure of passing food and the peristaltic movements of its 

 substrate. In our experience it attains greater numbers than any other 

 human intestinal protozoan. 



The Neuromotor System and Its Relation to the Symmetry op 

 THE Organism 



The neuromotor system of Giardia enterica is bilateral and consists 

 of the two centrosomes and the integrated fibrillar structures attached 

 thereto. These elements, attached to each centrosome or to the 

 blepharoplast, are as follows : an intranuclear rhizopla.st (intranuc. 

 rliiz., fig. B) passing to the central karysome (kary.), while peripherally 

 a rhizoplast (rhiz., fig. A) runs to the blepharoplast (bleph.) at the 

 anterior end of the axostyle (ax.), the parabasal body (par. h.), the 

 peristomal fiber [perist. /.), and four flagella {ft.). Giardia is bi- 

 nueleate and bilateral, but not diplozoie. The symmetries of the two 

 cells and their attendant neuromotor systems stand in a reversed rela- 

 tion, viewed from the standjDoint of other unicellular, poljnnastigote 

 flagellates, notably Ckilomastix. AVe find the neuromotor system 

 duplicated as to its constituent parts, but with those of the right side 

 arranged in the mirror image of those of the left. The constituent 

 elements of this system are duplicated throughout, except the com- 

 missures. Joining the two systems of the right and left sides is the 

 transverse commissure (trans, comm.) between the blepharoplasts. 



