114 rHE PROTOZOA 



part of the organism, and even diverse modifications of protoplasm, 

 such as the fine peripheral layer of alveoli {Pellicula of Butschli), and 

 the complex membranes of Euglena and Astasia (cf. Fig. 10, B). 

 The outer coatings as in all Protozoa, serving probably for the pur- 

 pose of protection, include houses and tests of all kinds which are 

 not a living part of the animal. In many cases they are simply jelly- 

 like coverings, which in many colony-forms also serve to keep the 

 individuals together (Uroglena, many Choanoflagellida, Fig. 59; see 

 also Fig. 25, p. 56). In other cases, the gelatinous mantle becomes 

 a tube, into which the organism can completely withdraw (some 

 Choanoflagellida). In still other cases, the jelly is apparently 

 hardened into a well-defined goblet or beaker-shaped cup with the 

 consistency of chitin (Codonceca, Epipyxis, Dinobryon, Salpiugoeca, etc.). 

 The relations of the firm case to the gelatinous mantle are shown in 

 forms like Codonazca, where the chitin-like urn-shaped cup may become 

 gelatinous (Fig. 60). The organisms are attached to the bottoms of 

 such goblet-shaped cups by a protoplasmic process, and in no case 

 does the cup fit the organism as tightly as a membrane. Colony- 

 forms also are frequent in these types, arising, in 

 the simplest cases, by a young individual attaching 

 itself to the edge of the parent test and there secret- 

 ing its own covering (Dinobryon, Fig. 61). The 

 majority of these colonies are attached, but Dinob- 

 ryon is a free-swimming form, usually found in the 

 clearest waters. 



Shells are distinguished from tests or houses by 

 the fact that they completely inclose the animal, the 

 so-called mouth-opening where the flagellum is in- 

 serted being the only aperture. Both tests and 

 shells are usually transparent and colorless, although 

 cllfaTa~\ C c'\Txv t ' ie y ma y ^ e colored by the presence of iron, as 

 [James Clark.] in Trachelomonas, Rliipidodendron, etc., where the 



shells, when present in any quantity, give a distinctly 

 red color to the water. The simplest shells are the cellulose cover- 

 ings of many Phytoflagellida, which, although lifeless, have the same 

 general appearance as membranes. The shell, which is frequently 

 protected by sharp spines ( Trachelomonas'), may be separated from 

 the plasm by a considerable space. It is bivalved in Phacotns, the 

 two parts being easily separated (Fig. 62). In one form only, Dis- 

 tcphanus speculum Stohr, there is a silicious skeleton which recalls the 

 latticed skeletons of Radiolaria (Fig. 63). 



The most highly differentiated of these outer coatings are found 

 in the Dinoflagellidia, where the cellulose shells are often composed 

 pf separate plates fitted together with the greatest nicety and often 



