CONJUGATION OP PROTOZOA 19 



fertDisation. In both cases the process is a decrease in the 

 number of individualities, as a preliminary to subsequent in- 

 crease. 



Professor Ischikawa, of Tokio, has given a very thorough 

 description of the phenomenon of conjugation in the phos- 

 phorescent flagellate Protozoa known as NoctUuca. Two pin- 

 head-like individuals unite for the purpose of conjugation. The 

 protoplasm of the two cells is mingled ; the nuclei, although not 

 altogether blended one with another, form a single karyokinetic 

 figure ; a karyokinesis sets in, in the course of which the chromatic 

 substance of the two conjugates is divided equally between the 

 nuclei of the two daughter organisms. Finally, as a result of 

 the karyokinesis, two distinct Nodilucas are formed. We see, 

 therefore, that, although the phenomenon of conjugation results 

 for a time in the diminution of the number of individuals, the 

 ultimate result is their multipUcation. 



A remarkable phenomenon presented by all multicellular 

 organisms, from the lowest to the highest, is the maturation of 

 the germ-ceUs, which is accompanied by a reduction of the 

 number of chromosomes to one-half of their original number. 

 In the case of the egg-cell, the original germ-ceU, through growth 

 and the doubling of the number of its chromosomes, gives rise to 

 the " ovocyte," or immature egg-cell (Fig. 2, B). This ovocyte 

 goes through two successive divisions. The result of the first 

 division is to divide the number of chromosomes into equal 

 halves. Thus, if we take four chromosomes as the normal 

 number for a given species, and suppose that number to have 

 been doubled in the course of the development of the original 

 germ-cell, we find that four chromosomes are, as a result of this 

 first division, ejected from the cell, so to speak. These four 

 chromosomes form the first " polar body," lying against the 

 exterior wall of the cell (Fig. 2, D, 'pg). The remaining half of 

 the chromosomes lie juxtaposed to the polar body, but within 

 the cell, forming a reduced nucleus. By a second division this 



2—2 



