64 MANUAL OF ZOOLOGY. 



II. ORDER SUCTORIA. This order includes a series of In- 

 fusoria of a very anomalous nature. In Acineta, which may 

 be taken as the type, the body is covered with a number of 

 radiating filamentous tubes, which are furnished at their 

 extremities with suctorial discs, and are capable both of exser- 

 tion and retraction. These retractile tubes both seize the prey, 

 and serve as vehicles for the ingestion of food ; hence the term 

 *polystome,' or many-mouthed, has been proposed for the 

 order by Professor Greene. 



III. ORDER FLAGELLATA. This order comprises those In- 

 fusoria which, like Peridinium, find their means of locomotion 

 in long, flexible, lash-like filaments, termed ' flagella ; ' cilia 

 occasionally being present as well. In some, as in Peranema 

 (fig. 10 e), there is only a single one of these appendages ; in 

 others, as in Anisonema, there are two flagella ; whilst in 

 Heteromastix and Pleuronema we have forms apparently transi- 

 tional between the Ciliata and the Flagellata, since both cilia 

 and flagella are present in these genera. In all their other 

 essential characters, the flagellate Infusoria do not differ from 

 the more typical members of the class. 



NOCTILUCA. Amongst the numerous organisms which con- 

 tribute to the phosphorescence of the sea,* one of the com- 

 monest is the animalcule known as Noctiluca (fig. 11), the 

 true position of which has not yet been determined. It is 

 nearly spherical in shape, having an indention, or ' hilum,' at 

 one side, close to which is fixed a long filament, probably used 

 in locomotion. The body consists of a ' cuticle ' and ' cortical 

 layer,' enclosing a central mass of sarcode. Near the filament 

 there is a minute oral aperture leading into a short digestive 

 cavity. A nucleus and vacuoles are also present. From the 

 presence of a mouth and from its general structure, Noctiluca 

 should be probably be looked upon as a flagellate Infusorian, 

 but it is placed by M. de Quatrefages amongst the Bhizopoda. 



AFFINITIES OF THE INFUSORIA. Though generally placed 

 amongst the Protozoa, of which they form the highest division, 



* The diffused luminosity of the sea is mainly due to the Noctiluca 

 miliaris ; but its partial luminosity is due to various phosphorescent animals, 

 amongst which are the Physalia utriculus (the Portuguese-man-of-war), 

 Medusa, Tunicata, Annelides, &c. The cause of phosphorescence is variously 

 stated, being supposed very generally to be caused by a process of slow 

 combustion analogous to that which takes place in phosphorus when ex- 

 posed to the atmosphere. Upon the whole, however, it appears that the 

 phenomenon is a vital process, consisting essentially in the conversion of 

 nervous force (or vital energy) into light ; just as the same force can be 

 converged by certain fishes into electricity. This transformation often 

 requires a special apparatus for its production, but it appears to be some- 

 times effected by the entire organism. 



