SEXUAL REPRODUCTION 215 



Now the chlamydomonas is an especially in- 

 teresting organism inasmuch as it responds 



Fig. 24. CMamydomonas media, sexual process. I. Sexual 

 cell (gamete). II. The same, somewhat more advanced. 

 III. The protoplasts, which have escaped from their 

 cellulose membranes, just in contact. IV. The fusion 

 nearly complete, note the two nuclei (dark spots), one in 

 each gamete. V. Complete protoplasmic fusion of two 

 gametes, but the two nuclei still distinct. VI. The zygote 

 after complete fusion, surrounded by a new membrane. 



with great precision to various changes in 

 external conditions which are able to influence 



