PHYSIOLOGY OF THE INVERTEBRATA. 27 



aperture there is a distinct tube — a short oesophagus, which is 

 closed at one end, for it does not dilate into a stomach. 

 Although there is no further differentiation of this primitive 

 alimentary canal, it forms a distinct advance on the forms so 

 far described. The posterior end of the oesophagus is closed 

 by the protoplasmic mass of the cell. Food particles are 

 brought to the mouth by means of the vibrating flagellum or 

 flagella in the Infusoria Jiagcllata, or by tentacula in the 

 Infusoria tcntaculifcra, or by cilia in the Infiisoria ciliata. 



In Monas vulgaris, one of the FlagcIIata, the food is dashed 

 by a sudden jerk directly against the oral aperture or mouth, 

 and the base of the flagellum presses the food particles into it. 

 According to Cienkowsky, bacteria, micrococci, and other 

 forms, which constitute the food of the Manas, " are pulled 

 into the latter's neighbourhood by strokes of the flagellum "' ; 

 and Drs. Dallinger and Drysdale remark that certain forms 

 of the FlagcUata are most voracious creatures. "The 'field' 

 in their neighbourhood is rapidly cleared of dead and living 

 bacteria, simply devoured by them. It is probable that this 

 capacity for absorbing nutriment, which must give large 

 advantage in the struggle for existence, explains the amoeboid 

 condition so common at what will be seen to be such an 

 important period in the development of the monads."* 



Xodiluca (Fig 3, a) is another genus of the Flagdlata. It 

 is extremely abundant in the upper layers of the waters of 

 the ocean, " and is one of the most usual causes of the phos- 

 phorescence of the sea." Phosphorescence is associated with 

 the function of digestion or nutrition, for many micro- 

 organisms will not "phosphoresce" unless supplied with 

 certain foods.f Noctiluca is a free swimmer. It is globular 

 in form, and possesses a sttong flagellum. The central pro- 

 toplasmic mass is connected by many radiating filaments 

 with the external layer, and contains a gastric or food 



* See Drs. Dallingei* and Drysdale's paper in Monthly Microscoj/kal 

 Journal, 1875, p. 194. 



t Dr. A. B. Griffiths' book : Jlcscarches on Micro-Orfjanisms, p. 165. 



