II 



PHYLUM PROTOZOA 



73 



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

 in some genera (9, g} 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 



Fro. 54. HsematoCOCCUS pluvialis. A, motile stage ; B, resting stage ; C, D, two modes 

 of fission ; E, Hcematococcns lacustris, motile stage ; F, diagram of movements of flagellum ; 

 chr. chromatophores ; c. vac. contractile vacuole ; c.v. cell-wall ; mi. nucleus ; uu'. nucleolus ; 

 pyr. pyrenoids. (From Parker's Biology.) 



marine Flagellates have siliceous skeletons similar to those of the 

 K/adiolaria, 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 RJiipido- 



