STRUCTURE OF AC I NET A 87 



Suctoria 



The small Acinetan drawn from life on Plate III. Fig. 5 

 was first found by my pupil Herr Lauterborn in his fresh- 

 water aquarium. Since I did not make a closer study 

 with regard to its systematic position, I am unfortunately 

 not in a position to determine it more accurately. For the 

 most part, it recalls Claparede and Lachmann's Acineta 

 notonectw, which I referred to the genus Solenophrya in my 

 work on Protozoa (q. v. p. 1930) ; our form possesses, however, 

 in contrast to that of Claparede, a distinct, though very short 

 stalk, and did not live on Notonecta but was fixed to particles 

 of dirt. This small, very transparent Acinetan permits the 

 structural relations of the protoplasmic body to be made 

 out very clearly in the living condition. The protoplasm 

 is completely reticular, and the width of the meshes of the 

 reticulum is about the same through the whole body. The 

 nodal points are not excessively prominent. The most 

 external layer of meshes, that which lies under the somewhat 

 pellicle-like external border of the surface, is everywhere 

 directed radially to the surface, and thus forms a distinct 

 alveolar layer (alv). Similarly, a radiate border of the same 

 kind is also formed round the macro-nucleus (mn\ which lies 

 nearly in the centre of the body, as well as round the 

 apically placed contractile vacuole (cv). The latter lies at 

 some depth under the apex, opening by a relatively long 

 efferent canal, which passes downwards from the apex into 

 the protoplasm. The wall of this canal appears like a dark 

 pellicle, and in any case is somewhat thicker and denser than 

 the pellicle of the surface of the body. Small nodal points 

 in the wall of the canal form the points of attachment for 

 the adjacent meshes of protoplasm, which are disposed at 

 right angles to the canal. In the protoplasm of the body, 

 dark, strongly refractile granules are deposited, varying in 

 size from such as are very minute to others which are 

 coarser. These granules are more especially collected in 

 certain spots, e.g. in the neighbourhood of the contractile 

 vacuole. 'The largest of them show a somewhat broad, 

 dark border. In the case of the smaller, it can always be 



