72 MANUAL OF ZOOLOGY. 



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 Hetero- 

 mastix and Pleuronema we have forms apparently transitional 

 between the Ciliata and the Flagellata, since both cilia and 

 flagella are present in these genera. In all their other essen- 

 tial 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, 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," en- 

 closing 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 pro- 

 bably be looked upon as a flagellate Infusorian, but it is placed 

 by M. de Quatrefages amongst the Rhizopoda. 



AFFINITIES OF THE INFUSORIA. Though generally placed 

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

 the position of the Infusoria cannot be looked upon as defi- 

 nitely settled. There is a growing opinion amongst competent 

 authorities that the Infusoria should be entirely removed from 

 the Protozoa, and that they should be placed amongst the An- 

 nuloida, having their nearest allies in the Turbellarian Worms. 

 If this change be carried out, the Infusoria and Rotifera, which 

 older naturalists grouped together, and which modern ob- 

 servers have placed widely apart, will be again brought nearly 

 together. If the sponges also should be removed from the 



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

 miliaris ; but its partial luminosity is due to various phosphorescent ani- 

 mals, 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 

 converted 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. 



