76 



ZOOLOGY 



SECT. 



(see Sect. IV.) in general form (Fig. 53, 11), being branched colonies 

 composed of a number of connected monads, each enclosed in a 

 little glassy lorica ; or green (chlorophyll-containing) zooids are 

 enclosed in a common gelatinous sphere, through which their 

 flagella protrude (12) ; or tufts of zooids, reminding us of the 

 flower-heads of Acacia, are borne on a branched stem (13). In 

 Volvox (Fig. 58) the zooids of the colony are arranged in the form 

 of a hollow sphere, and in Pandorina (Fig. 56) in that of a solid 

 sphere enclosed in a delicate shell of cellulose. Lastly, in Rhipido- 

 dendron (Fig. 53, 14) a beautiful branched fan-shaped colony is 



FIG. 56. -Pandorina morum. A, entire colony ; B, asexual reproduction, each zooid 

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

 tion of gametes ; O, zygote ; H K, development of zygote into a new colony. (From 

 Parker's Biology, after Goebel.) 



produced, the branches consisting of closely adpressed gelatinous 

 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. 55) and Euglena (Fig. 52), for instance, 

 divide while in the encysted condition ; Heteromita and other 

 saprophytic forms while actively swimming : in the latter case the 

 division includes the almost infinitely fine flagellum. 



In correspondence with their compound nature, the colonial 



