74 



ZOOLOGY 



SECT. 



dcndron (Fig. 52 , 

 the 



14) a beautiful branched fan-shaped colony is 

 produced, the branches consisting of closely adpressed gelatin- 

 ous tubes each the dwelling of a single zooid. 



Binary fission is the ordinary mode of asexual multiplication, 

 and may take place either in the active or in the resting condition. 

 Haematococcus (Fig. 54) and Euglena (Fig. 51), for instance, 

 divide while in the. encysted condition ; Heteromita (Fig. 57) 



Fia. 55. Pandorina mo rum. A, entire colony; B, asexual reproduction, each zopid 

 dividing into a daughter-colony ; C, liberation of gametes ; D F, three stages in conjugation 

 of gametes ; G, zygote ; H- -K, development of zygote into a new colony. (From Parker's 

 Biology, after Goebel.) 



and other saprophytic forms while actively swimming : in the 

 latter case the divison includes the almost infinitely fine flagellum. 

 In correspondence with their compound nature, the colonial 

 genera exhibit certain peculiarities in asexual multiplication. In 

 Vinobryon (Fig. 52, 11) a zooid divides within its cup, in which 

 one of the two products of division remains ; the other crawls out 

 of the lorica, fixes itself upon its edge, and then secretes a new 

 lorica for itself. In Pandorina (Fig. 55) each of the sixteen zooids 

 of the colony divides into sixteen (B), thus forming that number of 

 daughter-colonies within the original cell- wall, by the rupture of 



