THE ALGAE 



63 



physiological difference between these sexual coenobia although they all 

 look alike. 



Gametes from one type of coenobium fuse only with those of another. 

 The zygote so formed is at first quadriflagellate, it comes to rest and rounds 



Daughter colony 



Fig. 38.— Go»n/w sp. Colony in process of 

 asexual reproduction. Daughter colonies 

 in various stages of development, one being 

 already completed. 



off. A membrane is formed and a prolonged period of rest may follow. On 

 germination the zygote divides to produce four cells which form a plate, and 

 from each of these a fresh sixteen-celled coenobium is produced. It is 

 probable that the reduction division occurs during the first two divisions of 

 the zygote, for it has been shown that there is 

 a sexual segregation at this stage whereby two 

 of the daughter coenobia are sexually distinct 

 from the other two. 



Pandorina 



The colony consists of sixteen cells, each like 

 a single Chlamydomonas cell (Fig. 39). The cells 

 are rather pyramidal in shape and are arranged -pic. 

 in an oval group with their pointed ends inwards. 

 They are closely packed together, and the whole 

 coenobium is surrounded by a mucous investment. 

 Each individual cell has two widely divergent flagella, 

 of which the whole colony is propelled along, generally with 

 anterior end, in the cells of which the eye-spots are larger 

 developed. 



3g. — Pandorina morum. 

 Stained preparation of a 

 colony showing the cell 

 nuclei. 



by means 



a definite 



and better 



