240 GARY N. CALKINS. 



scribed by Schaudinn. In his preliminary paper this brilliant 

 observer does not go into the details of the process but states 

 categorically that the male nucleus contains only four of the 

 typical eight somatic chromosomes, while the female nucleus con- 

 tains a similar four in the shape of tetrads formed by the trans- 

 verse division into four parts of a longitudinally split spireme 

 thread, which are reduced to four single chromosomes by two 

 successive divisions, one a reducing the other an equation divi- 

 sion. Cytologists everywhere are waiting for a confirmation and 

 for a more definite description of this remarkable process which 

 thus resembles very closely the maturation processes of certain 

 metazoa. Other instances of reduction in protozoa have been 

 given from time to time, and are quite sufficient to show that 

 maturation phenomena are as widespread in protozoa as in other 

 forms of life and that their underlying significance is as wide as 

 the entire field of biology. The infusoria perhaps more than other 

 forms of protozoa are generally cited in this connection. Here 

 Maupas early showed that of the divisions of the micronucleus of 

 Parameciutn caudatum one persists to form the functional male 

 and female pronuclei, while the other three atrophy and disap- 

 pear in the cytoplasm. Schaudinn showed that in Heliozoa one 

 daughter-nucleus which he compared with a polar body is 

 thrown off to disintegrate and disappear in conjugating Acti- 

 nophrys, while Hertwig showed that two such bodies are cast off 

 by conjugating individuals of Actinosphaerium. 



In none of these cases has the finer details of chromosome 

 formation been sufficiently described, and the number of chromo- 

 somes has rarely been counted or the actual reduction made 

 out. Hertwig somewhat doubtfully claimed that the number in 

 Paramecium is reduced from eight or nine to four or six, but 

 there certainly must have been a mistake in the interpretation of 

 what constitutes the chromosome in this case, for the actual 

 number is many times greater than what he gives. One of the 

 graduate students at Columbia, Miss Cull, has worked with me 

 the past year on the formation of the chromosomes during the 

 conjugation period of P. caudatum, and although our results on 

 the maturation divisions are not yet ready for publication, we 

 have proved that the history of the chromatin in the early period 



