658 



charge takes place in the same way under normal conditions as in the 

 compressed specimens, it is necessary to watch free-moving indivi- 

 duals, and under these conditions the observations are difficult and 

 require much time and patience, for the Paratnecia are rarely in the 

 proper position for observation at the moment of discharge. But by 

 spending some hours on this, I was able to observe the discharge many 

 times on free, uncompressed specimens, so that there is no question 

 but that the phenomena shown by the compressed animals are normal. 



By the use of this method I have observed the discharge of the 

 contents of the contractile vacuoles in a number of Infusoria and 

 Rotifera, including, in the former group, Paramecium^ Nassula^ and 

 Oxy tricha \ in the latter group, Hydatina senta ^ DiascMza, and Pliilo- 

 dina. I regret that I have had no opportunity to study favorable exam- 

 ples of Amoeha from this point of view. Even in case the vacuoles 

 are discharged to the outside in Amoeba^ observation of the fact will 

 doubtless be difficult, since the vacuole is probably usually discharged 

 on the upper surface of the animal, where the contents would be 

 invisible. 



The use of India ink (Chinese ink) rubbed up with water for such 

 purposes as that indicated and for observation of ciliary currents I 

 have found much preferable to the carmine or indigo commonly em- 

 ployed. The India ink is much finer and darker and absolutely without 

 chemical action. Attempts have been made before to observe the 

 discharge of the contractile vacuole by the use of carmine or indigo; 

 the usual negative result I believe to have been due the larger granu- 

 les of these substances, rendering it hardly possible to make so densely 

 opaque a mixture without destroying the fluidity of the water and in- 

 juring the animals. To see the discharged vacuolar contents, the 

 surrounding water must be almost solidly black, without injury to 

 the animals: this is easily attained with the India ink. 



Zoological Station, Naples, Italy, April 27, 1904. 



II. Mitteilungen aus Museen, Instituten usw. 



1. Naturvetenskapliga Studentsällskapet, Upsala. 



Zoologische Sektion. 



(Schluß.) 

 Sitzung den 27. Februar 1903. 

 I. Trägardh, cand. phil,, teilt den Fund von Polynema natans Lubb. 

 mit. Er bestätigt, daß Polynema sich eines gut entwickelten Tracheensystems 

 erfreut, was von andrer Seite bestritten worden war. 



Im Zusammenhang hiermit wurde eine Darstellung der aquatischen 

 Hymenopteren gegeben. 



