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 diflferentiation 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 

 ilagella in the Infusoria flagellata, or by tentacula in the 

 Infusoria tentaculifera, or by cilia in the Infusoria ciliata. 



In Manas vulgai-is, one of the Flagellata, 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 Gienkowsky, bacteria, micrococci, and other 

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

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

 and Drs. Dallinger and Drysdale remark that certain forms 

 of the Flagellata 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."* 



Nodiluca (Fig 3, a) is another genus of the Flagellata. 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, t A'bc^itea is a free swimmer. It is globular 

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

 toplasmic mass is connected by many radiating filaments 

 with the external layer, • and contains a gastric or food 



* See Drs. Dallinger and Drysdale's paper in Monthly Microscopical 

 Journal, 1875, p. 194. 

 t Dr. A. B. Griffiths' book : liesearcliea on Micro- Organisms, p. 165. 



