CYTOLOGY OF SACCHAROMYCES CERVICL-E. 437 



of the formerly supposed cases of amitosis have been shown to be 

 merely simulations of it. Some of the authorities in this field, 

 however, are willing to elevate the Protozoa to essentially the 

 same position as Metozoa in this respect. Kofoid (1923) says: 

 "In the first place amitosis as described in the Protozoa is either 

 a pathological or degenerative process, as it is in the Metozoa, 

 or it is based on a partial account of the normal process of 

 mitosis in which the nuclear membrane remains intact throughout 

 the whole process, as it does in the flagellates and rhizopods, and 

 in its anaphases presents a superficial resemblance to pathological 

 amitosis. The persistence of the nuclear membrane in no way 

 interferes with the occurrence of chromosomes constant in number 

 and kind. In other words the doctrine of chromosome con- 

 tinuity, in so far as amitosis is concerned, is no more affected in 

 the Protozoa than in the Metazoa." The nuclear division 

 (promitosis) of many of the lower protozoa is unquestionably 

 very different from the mitotic division exhibited by higher 

 plants and animals, but it seems likely that in all cases it is 

 a simplified form of mitosis and is entirely unrelated to amitosis, 

 even though it does superficially resemble it. 



It seems as though the difficulty of studying nuclear division 

 in any form is responsible for the persistence of investigators in 

 describing it as amitotic. The tapeworm Monezia offers an 

 example of this (Child, 1911). Yeast belongs in the same 

 category, and we should realize the extreme difficulty of in- 

 vestigating this problem in yeasts by considering the minute 

 size of the cells and the fact that for some time there was a 

 heated controversy as to whether or not they even possess a 

 nucleus. Some of those who took the affirmative, as has since 

 been proved, were describing structures which belong to the 

 cytoplasm. Wager (1898) and Wager and Peniston (1910) 

 described as the nucleus, the actual nucleus, the vacuole, and a 

 part of the metachromatic material surrounding the nucleus and 

 vacuole. The division of this compound structure was described 

 as amitotic in the case of budding and by an "intermediate step 

 in karyokinesis " in the case of spore formation. This account 

 of the indirect division of a cytoplasmic vacuole is comparable 

 to the early figures of mitosis of the parabasal body (kineto- 



