1915] Kofoid and Christiansen: On Giavdia muris (Grassi) 45 



The evideuce iudicative of maturation is restricted to (1) progressive 

 fusion (figs. 61-63), (2) differences in sizes of nuclei suggesting 

 reduction (figs. 62, 63), and (3) possible reduction of the amount of 

 chromatin. There is no satisfactory evidence of a reduction of the 

 )tumher of chromosomes from four to two (fig. 63). If this inter- 

 pretation is correct, figure 61 represents encysted gametocytes, figure 

 62 gametocytes II after the first maturation division with marked 

 nuclear reduction in size in the first polar nuclei, and figure 63 the 

 completion of maturation in the upper pair of nuclei with two j^airs 

 of smallest nuclei representing the divided first polar nuclei, two 

 larger nuclei representing the second polar nuclei and the two gametic 

 nuclei still with four chromosomes each. The lower individual is still 

 in the stage of gametocyte II. It is obvious that gametes thus formed 

 would be hinuclcate and that a double zygote would result from 

 gametic union. This fact and the apparent absence of reduction of 

 chromosomes militate against the sexual interpretation. 



The final and only conclusive proof of this interpretation will l)e 

 the observed sexual behavior of the resulting gametes. Of this we 

 have no evidence. The possibility of multiple fission (cf. figs. 63 and 

 64 noting distribution of nuclei in both) is open, and the differences 

 in nuclear size (figs. 62, 63) might be merely pathological and the 

 occurrence of free pairing individuals (fig. 55) mere accidental arte- 

 facts. The internal evidence (except in the matter of a reduction 

 division) in favor of the sexual interpretation is both normal and 

 consistent as far as it goes, but is very incomplete and therefore incon- 

 clusive. The occurrence of sexual reproduction in Giardia muris and 

 G. microti is therefore very tentatively suggested. We have no satis- 

 factory evidence that the maturing "gametocytes" are sister cells or 

 that autogamy occurs. 



Summary 



Giardia muris occurs in culture mice (gray and white), and in 

 Peromyscus, but was not found in Microtus; neither it nor other species 

 were found in culture rats, Belgian hares, or coyotes, feeding where 

 Peromyscus was taken. It causes chronic enteritis, especially in young 

 hosts, with inflation and yellowish color of inte.stine. 



The normal trophozoite has a single axostyle, not two as heretofore 

 described, an integrated neuromotor apparatus with fibrillar connec- 

 tions joining the karyosomes, centrosomes, blepharoplasts, flagella. 



