CYSTOPLAGELLATA. 35 



Fani. 3. Dinophysida. Phalacroma Stein ; Dinojjhysis Ehrb. ; Amphisolenia 

 Stein ; Ornithoccrcus Stein ; Histioncis Stein. 



Fani. 4. Polydinida, with several transverse grooves and flagella ; naked. 

 Polykrikos Biitschli. 



Order 4. SILICOFLAGELLATA.* 



Marine mastigqphora irilli one flayelluiii- and a latticed silicious cap 

 on one side of the hod;/. 



The forms included in this order were formerly regarded by some 

 naturalists as Radiolaria, on account of their silicious latticed- 

 skeleton, and by others as parts of the skeleton of Radiolaria (large 

 species of Plw>o<1ai-ia). Their soft parts were imperfectly known, 

 owing to the fact that they are small, exceedingly sensitive to adverse 

 influences, and consequently very difficult to get under observation 

 in the living state. The body lies within the skeleton, and contains 

 some small brownish-yellow spherical bodies. There is a nucleus in 

 the centre of the protoplasm, bounded by a membrane, and con- 

 taining a nucleolus; it has been called the central body. There is 

 one long vibratile flagellum. The body is without a bounding 

 membrane, and there are no pseudopodia. The reproductive processes 

 are unknown. The skeleton consists of hollow silicious rods, and 

 has the form of two circles united by rods ; it invests the body in 

 a cap-like manner. 



Fani. Dictyochidae, with the characters of the order. Mesocena Ehrb. ; 

 Didyocha Ehrb. ; Distephanus H. ; Cannopilus H. 



Order 5. CYSTOFLAGELLATA (RHYNCHOFLAGELLATA). 



Mastigoph&ra of large size with a single nucleus, reticular proto- 

 frfasni, and a stout membrane. 



Noctiluca is a nearly spherical form of large size (1 mm. in 

 diameter), and has on its ventral side a groove, called the peristome, 

 at the base of which is the elongated slit-like mouth. From the 

 anterior end of the peristome projects a large transversely striated 

 flagellum, sometimes called the tentacle, and a little further back 

 on the right side are two organs, the tooth and the lip. The 

 flagellum is a contractile organ and varies in form : it moves slowly 

 from side to side. The tooth is a protoplasmic projection, and 

 is probably actively movable. From the lip there projects forward 

 a smaller and vibratile flagellum. The greater part of the protoplasm 

 with the nucleus is aggregated on the ventral side at the base of 



* A. Borgert. " Ueber die Dictyochiden," etc. Z. f. w. Z., 51, 1891, p. 629. 



