202 NATURAL HISTORY OF BHOMPSTON POND. 



Actinosphaerium Echhornii (fig. 2) occurs fairly plentifully 

 floating amongst the vegetation. Its spherical body (clearly 

 divisible into endoplasm (a) and ectoplasm (b) is of a beautiful 

 glassy appearance and gives rise to an abundance of hair- 

 like pseudopodia (c). The endoplasm contains about two 

 hundred nuclei and usually several food vacuoles (d), 

 while in the vacuolated ectoplasm, the bases of the 

 axes and several contractile vacuoles (e) can be watched 

 even with a low power. Food is taken in, and the indigestible 

 residue cast out, at any part of the body. When an organism 

 touches the outstretched pseudopodia, the latter bend over 

 it (f), and, gradually diminishing in length, finally bring it to 

 the body, in which it is gradually embedded, but at last, as if 

 with a final effort of the pseudopodia, it is somewhat suddenly 

 engulfed. During an observation of forty minutes the 

 writer saw a single Actinosphaerium thus ingest two rotifers 

 and a diatom, while other pseudopodia were engaged in 

 combat with a relatively large water -flea (Chydorus sphaericus), 

 which, however, succeeded in escaping after a struggle lasting 

 one hour and twenty minutes ! 



A few specimens of a closely allied form, Actinophrys sol, 

 were found in samples of sediment from the centre of the 

 pond. It differs from the last it being much smaller (l-1000th 

 of an inch in diameter), in having one nucleus only, and 

 relatively fewer pseudopodia. 



Corticata is well represented in the pond by a vast variety 

 of organisms, which agree, however, in having the protoplasm 

 differentiated into a central fluid portion and a firmer cortical 

 layer, and further by possessing cilia (Ciliata). Ciliary action 

 is, perhaps, the most striking feature exhibited by these 

 organisms. The quickly repeated rhythmical movement of 

 bending down and regaining the original position of each 

 cilium gives the appearance of ripples comparable with the 

 waves in a cornfield. The cause of ciliary movement is 

 UNKNOWN,. Engelmann suggests that one side of the cilium 

 may be contractile and the other side elastic, while Schafer 

 likens it to amoeboid movement, suggesting that the motion 



