FEEDING REACTIONS IN DILEPTUS GIGAS. 131 



two distinct processes involved in feeding: (i) The capture of 

 food and (2) the ingestion of food. In feeding on motile organ- 

 isms both processes are involved, but when feeding on non-motile 

 substances only the latter process is involved. When feeding on 

 motile forms the prey is first paralyzed, and in many cases where 

 this is only temporary the cytoplasm of the prey is locally seri- 

 ously affected. In some forms that part of the protoplasm affected 

 is constricted off, while in other forms the entire organism is 

 affected. In this non-motile condition the prey is carried passively 

 by the ciliary current to the buccal cavity and there ingested as 

 described above. The trichocysts are evidently the structures 

 which enable Dilcptus to capture living prey and make the feeding 

 process of this organism so complicated. The remaining part of 

 the paper will be devoted to observations and discussion as to their 

 nature and function. 



5. TRICHOCYSTS. 



The nature and function of trichocysts has long been a debated 

 question and even today most authors admit that we know very 

 little about them except in the case of one or two organisms which 

 have been studied very extensively, and even here there is much 

 controversy. 



Mitrophanow ('04) maintains that the trichocyst consists of a 

 viscid fluid contained in a cavity in the ectoplasm, whence it is 

 expelled by a sudden contraction of the ectoplasm and stiffens to 

 form a solid thread under the action of the water medium. 



Schuberg ('05), however, denies this and maintains that the 

 unexploded trichocyst is a spindle-shaped body with a fine hair- 

 like process at its outer end which reaches to the pellicle, and that 

 when it explodes this material forms into a fine thread-like sharp- 

 pointed rod, often showing a cap-like swelling at one end. 



Calkins in 1901 maintained that there are only two types which 

 have been definitely made out a rod-like form as in Lo.vophyllum 

 and a spindle-shaped form as in Paramecium. He also stated that 

 "when protruded from the body they are apparently of the same 

 size and shape as when within the ectoplasm." In 1910, however, 

 the same author wrote concerning trichocysts in general (p. 27), 

 " when the organism is irritated the contents of the capsules are 



