38 University of California Publications in Zoology [Vol. ig 



connect it structurall}' b^' attachment to the neuromotor apparatus, 

 but it lies in close conjunction with it, usually so as to obscure it, and 

 stains in the same manner. Its position, the varying shapes and 

 dimensions it as.sumes in life and in stained preparations (pi. 5. figs. 

 1. 4) indicate a neuromotor function. 



Two areas distingui.shed by relative lack of stainability are to be 

 noted, an anterior halo {ant. halo. fig. A) in the median line above 

 and anterior to the blepharoplasts, and a triangular halo (tri. halo) 

 about the axostyle posteriorly between the intracytoplasmie parts of the 

 postero-lateral flagella. Their function, if any, and significance are 

 wholly problematical. 



Binary Fission 

 This process occurs in both encysted and non-encysted individuals. 

 It is probable that many of the incipient phases observed may be 

 antecedent in some case.s to multiple mitosis, following binary mitosis. 

 The occurrence of two mobile detached individuals in one cyst is open 

 to the interpretation as the result of binary fission. Binary fission is 

 abundant in our slides in the non-encysted individuals, especially in 

 its early phases. It seems probable, therefore, that the previous 

 failure to detect it is not due to its non-occurrence. Binary fission 

 consists of two processes, mitosis, involving the nucleus and the extra- 

 nuclear neuromotor apparatus, and plasmotomy, independent of and 

 subsequent to mitosis, involving the cytoplasm. 



I\IiTOsrs 

 This process involves blepharoplasts, axostyle, and flagella, as well 

 as the nucleus. The division of each follows no fixed chronological 

 .sequence, multitudinous minor variations in the relative order of 

 division being apparent in our material. In a general way the sequence 

 of events is as follows : Division of the blepharoplasts, of the axostyle, 

 of the anterior flagella, enlargement of the karyosome, appearance of 

 eight chromatic masses, their arrangement in the form of a split skein, 

 the division of the eentrosome and formation of the paradesmose 

 between the daughters, the fusion of the eight chromatic masses into 

 four masses or chromosomes, the appearance of these in the equatorial 

 plate of the intranuclear spindle, migration of daughter chromosomes 

 towards the poles of the spindle, division of the parabasals, nuclear 

 constriction, and much later, plasmotomy. The formation of the other 

 new flagella is subject to considerable variation in relative chronology. 



