ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 409 



mouth and ingested. Of two particles within the funnel at the same 

 time one may be thus rejected while the other is ingested. Selection 

 thus occurs not only from among particles reaching the pouch succes- 

 sively, but from a large number reaching the pouch at once. 



Stentor distinguishes very accurately between organisms and indi- 

 gestible particles, and between different kinds of organisms. It discrimi- 

 nates more restrictively when almost satiated than when very hungry. 

 Tlie amount of a given substance ingested depends upon what other 

 substances are present. It was not found that Stentor became lastingly 

 "educated" to reject certain kinds of food. 



Stentor selects its food upon a tactrial basis, reacting to physical, 

 not chemical properties. Stentor in a condition of satiety differs in 

 many respects from Stentor in a condition of hunger, e.g. in the activity 

 of the membranellse and in responsiveness. The amount of food at a 

 given time is not an accurate index of satiety, which depends also upon 

 what recent stimuli have been received. 



Species of Paramoecium.* — L. L. Woodruff finds that a large majority 

 of the individuals of P. aarelia and P. caudatum can be distinguished 

 on the basis of shape alone or of size alone. Tlie power of reproduction 

 and the general vitality of the two species are practically identical. The 

 macronucleus is subject to such great variation that it affords no dia- 

 gnostic feature. But the micronuclear apparatus affords crucial diagnostic 

 characters. In. prolonged cultures the species breed true and should be 

 regarded as quite distinct. 



Fauna of Hay Infusions.f — L. L. Woodruff has studied the origin 

 and sequence of Protozoan faunas in hay infusions. Ordinary hay added 

 to tap-water will not produce a representative Protozoan fauna. Air, 

 water, and hay are all sources from which the Protozoa of infusions are 

 derived, and increase in importance in the order stated. Of the three, 

 however, air is practically a negligible factor in seeding infusions. 



In hay infusions, seeded with representative forms of the ciiief groups 

 of Protozoa, there is a definite sequence of dominant types at the surface, 

 namely Monad, Colpoda, Hypotricliida, Paramoecium, Vorticella and 

 Amoeba. The sequence of maximum numbers and of disappearance is 

 identical with that of appearance, except that apparently the position of 

 Amoeba advances successively from the last (sixth) place to the fifth 

 place and then to the fourth place. 



A definite sequence of forms is not apparent at the middle or bottom 

 of the infusions. The middle of the infusions is tenanted chiefly by a 

 free-swimming population brought there by an overcrowding at the top 

 or bottom. All of the Protozoan forms considered (except Amoeba) are 

 chiefly surface dwellers, and it is evident that when they pass their 

 greatest development at the surface this maximum is seldom approached 

 again and their cycle is practically over. The major rise and fall in 

 numbers are usually about equally rapid, though the final disappearance 

 of an organism may be long deferred. 



The appearance of any of the Protozoan forms under consideration 



* Journ. Morphol., xxii. (1911) pp. 223-37 (1 fig.), 

 t Journ. Exper. Zool., xii. (1912) pp. 205--64 (15 figs). 



Aug. 21st, 19 V2 2 f 



