PHYLUM PROTOZOA 



73 



In Euglena, as we have seen, there is a short, narrow gullet, and 

 in some genera (9, y) this tube becomes a large and well-marked 

 structure. 



Skeleton. While a large proportion of genera are naked or 

 covered only by a thin cuticle, a few fabricate for themselves a 

 delicate chitinoid shell or lorica (10, /.), usually vase-shaped and 

 widely-open at one end so as to allow of the protrusion of the 

 contained animalcule. In the chlorophyll-containing forms there 

 is a closed cell-wall of cellulose (Fig. 54, c.w.). One group of 



S 



Fio. 54. HsetnatOCOCCUS plnvialis. A, motile stage ; B, resting stage ; C, D, two modes 

 of fission ; E, H&matococcv.s lacustris, motile stage ; F, diagram of movements of flagellum ; 

 clu: chromatophores ; c. rac. contractile vacuole ; c.v. cell-wall; nv.. nucleus; nu'. nucleolus; 

 r/i-. pyrenoids. (From Parker's Blolopy.) 



marine Flagellates have siliceous skeletons similar to those of the 

 Radiolaria, with which they were originally classed. 



In many genera colonies of various forms are produced by 

 repeated budding. Some of these are singularly like a zoophyte 

 (see Sect. IV.) in general form (Fig. 52, 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. 56) the zooids of the colony are arranged in the form 

 of a hollow sphere, and in Pandorina (Fig. 55) in that of a solid 

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



