PLATE 7 



Binary and multiple fission in Giardia. All figures of G. muris (Grassi) 

 from culture mice unless otherwise stated. X 2720. 



Fig. 31. Early phase of multiple fission, in late prophase of second division. 

 Daughter zooids with full equipment of organelles, blepharoplasts and axostyles 

 divided for second division, chromatin in split skein condition. Probably twisted 

 at the protoplasmic bridge. 



Fig. 32. Dorsal view of about the same stage but of much smaller size. 



Fig. 33. The same stage, protoplasmic connection reduced. 



Fig. 34. The same in late prophase. From Peromyscus. 



Fig. 3-5. — Cyst with one individual with nuclei showing four chromosomes, 

 no jiarabasals, peristome disappearing, and chromidial masses appearing in the 

 cytoplasm. The intracytoplasmic parts of the antero-lateral and postero- lateral 

 flagella are still visible, especially the former. 



Fig. 36. The same stage. Chromatin massed in bifid central karyosome, 

 chromidia increased, peristome gone, antero-lateral flagella displaced. 



Fig. 37. Anaphase of first division of encysted individual, four chromosomes 

 in two masses at either pole, parabasal persisting, small amount of chromidia. 



Fig. 38. First division of G. microti completed, posterior peristomes and 

 intracytoplasmic parts of antero-lateral and postero-lateral flagella persisting 

 but displaced, quadripartite central karyosome, few chromidia. From Microtus. 



Fig. 39. Later stage with extranuclear organelles in dissolution, with con- 

 siderable chromidial accumulation in the cytoplasm. From Peromyscus. 



Fig. 40. Problematical stage, possibly pathological, in anajjhase of second 

 division, no cj'st wall, organelles in dissolution, much chromidial material. From 

 Peromyscus. 



Fig. 41. "Conjugation cyst," evidently containing two individuals with 

 ends iu reversed position in each of which the nuclei have completed the first 

 division, and in which a second division is approaching. The difference in 

 appearance of the nuclei is indicative of position only, not of structure. From 

 Peromyscus. 



Fig. 42. Cyst with sixteen nuclei bilaterally arranged. Axostyles, intra- 

 cytoplasmic parts of antero-lateral and postero-lateral flagella persisting but 

 disorganized, some chromidial material, peristome gone. Four chromosomes. 



Fig. 43. Cyst with sixteen bilaterally grouped nuclei each with very small 

 central karyosome, all cytoplasmic organelles gone e.xcept axostyles and postero- 

 lateral flagella, many rounded chromidial masses. From Peromyscus. 



Fig. 44. Cyst with sixteen nuclei each showing four chromosomes, bilateral 

 arrangement not evident, blepharoplasts, axostyles, and intracytoplasmic parts 

 of antero-lateral and postero-lateral flagella persisting, two masses of chromidial 

 spheres. From Peromyscus. 



Fig. 45. Free individual of G. microti in early stage of multij>le fission, all 

 organelles intact, no chromidia, four axostyles indicated and eight nuclei present, 

 bilateral arrangement of nuclei disturbed. From Microtus. 



Fig. 46. The same stage of G. microti with two axostyles and nuclei in 

 bilateral arrangement, two chromidial masses present. From Microtus. 



Fig. 47. An earlier stage of multiple fission in free individual of G. muris 

 in prophase (lower nuclei) and anaphase (upper nuclei) of second division, two 

 axostyles present, posterior peristome gone, anterior peristome degenerate, 

 diffuse chromidial masses present. 



Fig. 48. Somatella of G. muris in 8-nucleate, 4-zooid stage, with nuclei in 

 late prophase of third division, the two zooids to the left in end-to-end position, 

 the two to the right parallel to each other. From Peromyscus. 



Fig. 49. Somatella of four small zooids, probably a disintegrative phase of 

 a 16-nueleate, 8-zooid stage. From Peromyscus. 



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