278 



THE PROTOZOA 



highly differentiated as regards forms and species. The vast majority are 

 pelagic in habit, and constitute an important element of the plancton fauna, 

 both marine and fresh-water. A certain number of species are adapted to 



parasitic life. They are divided into two 

 orders. 



ORDER I. : ADINIDA (Prorocentraceae). 

 Primitive forms in which the typical peculi- 

 arities of Dinoflagellatc organization are not 

 fully developed. The body-envelope consists 

 of a bivalve shell without furrows. The two 

 flagella emerge through an aperture between 

 the two valves, and one flagellum projects' 

 freely into the water, while the other twists 

 round it at the base. Example : Prqrocentrum. 

 ORDER II. : DINTFERA. With the typical 

 characters of the subclass, as described above. 

 Families: (1) Oymnodinidae, without a well- 

 developed cuirass example : Qymnodinium ; 

 the marine genus Oxyrrhia (Fig. 123) is referred 

 to this family by Senn (358); it is holozoic 

 in habit. (2) Peridinidce, with a well-developed 

 cuirass made up of definite plates examples : 

 Qlenodinium (Fig. 120), Ceratiuru, Ceratocorys 

 (Fig. 121), Peridinium, etc. ; Pyrodinium 

 (Plate, 385) is remarkable for its intense phos- 

 phorescence ; at the hinder pole, between the 

 chromatophores, the cytoplasm contains a body, 

 the " Nebenkorper " of Plate, surrounded by 

 numerous oil-drops, which are perhaps the 

 seat of the luminosity. (3) Dinophysidae, 

 oceanic species with the cuirass divided by a 

 sagittal suture, often of extraordinary form 

 example : DinopJiysis, etc. (4) Blastodinidce, 



a family created by Chatton (366, 367) for certain parasitic forms ; such 

 are Blastodinium, an internal parasite of various copepods, and Apodinium 

 mycetoides, an ectoparasite of appendicularians (Fritillaria). The parasitic 

 vegetative form, without organs of locomotion, 

 gives rise by periodic segmentation of mother- 

 cells to successive generations of swarm-spores, >^Pi^$k fir 



FIG. 122. Peridinium diver- 

 gens : ventral view showing 

 the vacu&le-system. e.p., 

 The collccting-pusule sur- 

 rounded by a rosette of still 

 smaller pusules which open 

 into it ; s.p., the large sac- 

 pusule, or reservoir ; both 

 opening into the fundus (/.), 

 from which both the trans- 

 verse flagellum (<.), lying in 

 the annulus (a.), and the 

 longitudinal flagellum (I.), 

 arise. After Schiitt, from 

 Lankester. 



N 



which in their structure resemble Qymnodinium. 



SUBCLASS III. : CYSTOFLAGELLATA SEU 

 KHYNCHOFLAGELL ATA . 



This group comprises a small number of 

 forms all marine and pelagic in habitat. 

 Their chief peculiarity is that, like so 

 many other pelagic organisms of all classes, 

 the body is inflated, as it were, with 

 watery gelatinous substance, so that it 

 attains to a size which far exceeds the 

 actual bulk of the living substance con- 

 tained in it. In consequence of the 

 secondary increase in size, the powers of locomotion are feeble, and 

 these organisms float more or less helplessly on the surface of the soa. 



eat. 



FIQ. 123. Oxyrrhia marina, 

 Duj. P., Peristome ; N., 

 nucleus; f.v. food- 

 vacuoles ; ex., excretory 

 mass about to be ejected. 

 After Blochmann, from 

 Senn (slightly modified) ; 

 magnification 1,000. 



