1922] Kofoid^Swezy : Mitosis and Fission in Giardia enterica 213 



24, figs. 4-12). Thirdly, the neuromotor system is duplicated at the 

 time of mitosis (pi. 24, figs. 10, 11). The method of duplication is less 

 certain. This appears to take place by duplication of the centrosomes 

 and blepharoplasts by division, by the longitudinal division of the 

 axostyle and i)arabasal.s, the former from the anterior end posteriorly, 

 and by the splitting of the peristomal fiber from the posteromedian 

 end anteriorly. 



The question as to whether these organs split or are duplicated by 

 distal outgrowth of a new element whose growing distal end alongside 

 the old lies near or in contact with the older structure, is largely one 

 of interpretation. In the absence of free ends of new outgrowths and 

 of young or small axostyles and parabasals, the morphological evidence 

 favors the interpretation of splitting for these organs, though either 

 is possible. The equality of size and peripheral contact of the two 

 elements support the interpretation of splitting. 



There is, however, clear evidence in support of the view that the 

 flagella are duplicated by the outgrowth of one new set rather than 

 by splitting of the old. There is a new outgrowth of a pair of antero- 

 laterals at the prophase shortly after the division of the centrosome 

 and formation of the paradesmose (pi. 24, figs. 7-10, and text figs. 

 F-K) . The sprouting flagella when first seen (fig. P) form an inverted 

 V-shaped, anterior projection from the blepharoplasts, the apex of 

 which is the anterior node. It appears to involve the whole of the 

 transverse eommis.sure. This structure is figured by Simon (see 

 Hegner and Cort, 1921) but not interpreted as here stated. It is 

 typical of the prophase only. The anterior outgrowth continues until 

 the node is carried out near the parental one (fig. H) and the growing 

 flagella extend from it beyond the node in the laterally arched processes 

 which come ultimately to be dorsal to the older flagella. At no time 

 until the completion of the anterior progression of the node is there 

 even the semblance of origin by splitting. It is clearly a case of origin 

 by outgrowth of one new flagellum duplicating the parental one which 

 persists. The homologous flagellum of Chilomastix and the tricho- 

 monads also arises by new outgrowth. 



There is a suggestion of a similar sprouting process in the ventral 

 and posterolateral flagella in the fact that at the prophase there appear 

 deeply stained enlargements of the intracytoplasmic parts of the 

 posterolaterals near their junctions with the axostyles and on the axo- 

 styles at the points where the ventrals appear to join them. These 

 enlargements we interpret as local growth phenomena preparatory to 



