CHAPTER III 



GENERAL MORPHOLOGY: CYTOPLASMIC DIFFERENTIATION, 

 COLORATION, SURFACE DIFFERENTIATION 



Cytoplasimic Defferextiatiox. — The tribe GjTiinodiuioidae presents both 

 extremes of cytoplasmic complexity found within the Flagellata, its lower forms 

 having the simplicity of structure found in the lower flagellates, and its more 

 highly specialized ones being exceeded in complexity only by the TrichonA^n- 

 phidae. In most of the species no distinct ectoplasmic differentiation can be 

 detected, beyond the presence of a thin periplast surrounding the body (figs. 

 X, CC). Varying degrees of differentiation leading up from this simple type 

 may be found with its highest development sIioaati in the subgenus Pachydinium 

 of the genus Gijmuodhiium (fig. AA). 



A distinct ectoplasm is present in this subgenus showing a degree of special- 

 ization reached elsewhere only by the Ciliata. This, as appears in Gymnodinium 

 pachydermatnm (fig. AA, 5), consists of a relatively wide, clear, homogeneous, 

 double-contoured zone surrounding the endoplasm. Superimposed upon this 

 zone is an outer, alveolar layer, somewhat wider than the inner zone of homo- 

 genous ectoplasm. The outer facets of the alveoli are roimded and give to the 

 surface of the body a roughened, irregular contour. The alveoli are filled with 

 a clear homogeneous fluid of the same consistenev as that found in the inner 

 zone of ectoplasm. 



Correlated with this specialization of the ectoplasm is a relative complexity 

 of endoplasm shoA\Ti in the presence of radial rodlets, vacuoles, oil droplets and 

 refractive granules. In some species the radial rodlets seem to occupy definite 

 places in the plasma and are probal^ly intimately related to the metabolic 

 activity of the organism. They may be lacking in a few individuals and present 

 in others of the same species. Their usual location is near the anterior pore 

 and leading out towards the periphery of the body. They may sometimes be 

 observed streaming out from the pusule (fig. Y). 



In many other species showing a lack of ectoplasmic differentiation a zone 

 of short rodlets is often present in the peripheral region, closely packed together 

 and at right angles to the surface (fig. CC, 7). In end view these appear like 

 small vacuoles. These apparently have the same structure and greenish color 

 as the longer, centrally located ones, and evidently subserve the same or similar 

 purposes in the life economy of the organism. They are probably connected 

 with a saprophytic type of nutrition, since they are never present in forms 

 possessing ehromatophores. They are also absent generally in the more highly 

 specialized members of the Gymnodinioidae, such as CocModinium, and the 

 Pouchetiidae, where nutrition is probably holozoic throughout. 



[36] 



