770 MICROSCOPIC FORMS OF ANIMAL LIFE 



The name CUio-flagellata, and the definition of the group must 

 both be altered, now that Klebs and Biitschli have shown that what 

 was regarded as cilia in the transverse grooves of their bodies is 

 really a flagellum ; the name to be used is Dinoflagellata,. 1 Al- 

 though this group does not contain any great diversity of forms, yet it 

 is specially worthy of notice, not only on account of the occasional 

 appearance of some of them in extraordinary multitudes, but also for 

 their power of forming cellulose a property which is often thought 

 to be particularly characteristic of plants. The Peridiniuin observed 

 by Professor Allmaii in 1854 w:i> present in such quantities that 

 it imparted a brown colour to the water of some of the large ponds 

 in Phoenix Park, Dublin, this colour being sometimes uniformly 

 diffused, and sometimes showing itself more deeply in dense clouds, 

 varying in extent from a few square yards to upwards of a hundred. 

 The animal (fig. 590, A, B) has a form approaching the spherical, 

 with a diameter of from i^Voth to - 1 0(l th of an inch, and is 

 partially divided into two hemispheres by a deep equatorial furrow, 

 , whilst the flagellum- bearing hemisphere, A, has a deep meridional 

 groove on one side, 5, extending from the equatorial groove to the 

 pole, the flagellum taking its origin from the bottom of this vertical 



FIG. 590. Peridiniuni uberrimum: A, B, front and back views ; 

 C, encysted stage ; D, duplicative subdivision. 



groove, near its junction with the equatorial. The members of this 

 group vary considerably in their mode of taking food ; from the 

 researches of Bergh it would appeal- that those which are provided 

 with chromatophores have a plant-like mode of obtaining food, while 

 those which are without chromatophores are truly animal in their 

 method of alimentation. A 'contractile vesicle' has been rarely 

 observed ; but a large nucleus, sometimes oval and sometimes horse- 

 shoe-shaped, seems always present. The Peridinia multiply by 

 transverse fission (fig. 590, D), which commences in the subdivision 

 of the nucleus, and then shows itself externally in a constriction of 

 the ungrooved hemisphere, parallel to the equatorial furrow. They 

 pass into a quiescent condition, subsiding towards the bottom of the 

 water, and the loricated forms appear to throw off their envelopes. 

 There is reason to believe that conjugation obtains in certain cases : 

 Glenodiniutn cinctum has been observed by Professor Askenasy to 

 copulate, but the development of the zygote, as the product of copu- 

 lation may be called, has not yet been worked out. Some of the 

 Peridinia are found in sea- water, 2 but the most remarkable marine 



1 Or, more correctly, Dinomastigopliora, 



See F. Schiitt, ' Die Peridincen der Plankton Expedition,' Err/cbn. Plankton 

 Exped. 1895. 170 pp. and 27 pis. 



