SEXUALITY 



17 



surrounding themselves with a zone of protoplasm, form 4 or 8 

 ascospores. The zygospore is then transformed into an asc. In 

 many cases the fusion of gametes is not always complete and the 

 asc retains a median constriction, a remnant of the copulation canal. 

 It often happens that, in certain cases, the gametes remain individ- 

 ualized, and the asc may be constituted of two cells united by a copu- 

 lation canal. In this case, the ascospores are formed in groups of 

 2 or 4 in each cell. These are formed 

 especially when copulation takes place 

 between cells which, not being united, 

 are obliged to send out long projections. 

 With Sch. octosporus all of the steps 

 between complete and incomplete fusion 

 of gametes may be observed, but in the 

 two cases the result is the same and it 

 produces a zygospore. 



In a few rare cases the asc originates by parthenogenesis; this is 

 happening when one sees two gametes united by a canal in which the 

 wall has not been perforated, forming individually a parthogenetic asc. 



A very peculiar fact, and one which should be mentioned here 

 on account of its biological significance, is the copulation between 

 two adjacent parent cells or, as Schionning has described, between 



15. Various Stages in the 

 Copulation of Schizosaccharo- 

 myces octosporus as Observed 

 in Bottcher's Moist Chamber. 



a, 10 o'clock in the morning; 6, 1 

 o'clock; c, 2 o'clock; d, 5 o'clock; 

 e, 6 o'clock. 



Fig. 16. Copulation and Formation of the Asc in 

 Schizosaccharomyces octosporus (in Stained Preparation). 



two cells sprung from the same mother cell between two brother 

 gametes. It is a primitive characteristic which distinguishes this 

 copulation from the sexuality of more highly developed organisms. 



As a rule, almost all of the cells fuse two by two with the forma- 

 tion of the egg and more often between two adjacent cells in the 

 same colony. As each colony is composed of 15 or 20 cells, the 

 gametes are necessarily closely related. The same thing is true in 

 colonies made up of 2 or 3 cells which are able to copulate two by 

 two. One is able to follow under the microscope the formation of 



