Animal Evolution. 187 



Dinoflagellata. — These animals are phosphorescent 

 and possess a mouth, hence would seem to be highly 

 developed ; but as their cell-walls are composed of 

 cellulose, and their medulary protoplasm contains 

 chlorophyll, diatomin, and starch, they are closely 

 related to vegetals. 



The Ciliata have cilia or hair-like processes pro- 

 truding over the whole body. The cilia act as oars 

 or locomotor organs, or serve for introducing food 

 particles into the mouth. Some species contain 

 isolated individuals, while others constitute colonies. 

 One highly modified form (Thuricola valvatd) repre- 

 sents a tube fitted with a valve, like the door of the 

 "trap-door" spider's nest. In the most developed 

 species the cilia are modified and enlarged into 

 muscular appendages (setae) by which the animal 

 ambulates. 



The Rctiadaria constitute a connecting link be- 

 tween amorphous and symmetrical protozoa. Although 

 the reticularia are themselves shapeless, structureless, 

 and unorganised masses of protoplasm in their normal 

 manifestation, they project like an actinophrys out- 

 spreading rays of ephemeral pseudopodia, and secrete 

 skeletons of carbonate of lime, innumerable in pattern 

 and exceedingly elegant in design. They do not 

 resemble molluscs, for their shell is not external but 

 semi-external and internal ; sufficient to enclose the 

 animal when retracted, it is yet perforated by number- 

 less minute orifices through which the protoplasmic 

 rays project. 



