932 Transactions of the Society. 



tracted, but after a few minutes elongated itself, and spread out its 

 tentacles in all directions. The Trichodina took no notice of the 

 Hydra. Some settled themselves down in a quiescent condition, 

 whilst others would spin round with a concentric motion, after a 

 time again putting themselves in motion. If they struck against 

 the Hydra they recoiled, as it were, from the contact, and con- 

 tinued their course; hut at no time was there any adhesion to 

 show their ectoparasitic nature. After the lapse of an hour the 

 Hydra contracted itself, and gradually withdrew its tentacles until 

 they were mere points ; in a short time they disappeared entirely, 

 and decomposition set in; some of the Trichodina lived about 

 three hours afterwards, and then died. This experiment was 

 repeated at different times with similar results. 



It was otherwise, however, with the control experiment where 

 the Trichodina at once attached themselves to the Hydra. Both 

 lived for days, the former seeming as much at home on the tentacles 

 of the Hydra as on the branchiae of the larvae of Triton. 



I tried another experiment. I isolated five newts, placing 

 them in a dry bell-glass on some pieces of granite, and kept them 

 without food or water for twenty-one days. I did this to know 

 whether the fact of keeping them without nutriment would have 

 any effect on the existence of the Trichodina if found. Of the 

 five newts one died from starvation, and the others became very 

 torpid, huddled up together, and were in a very emaciated condition. 

 I killed two, and found that the viscera had shrunk considerably, 

 more especially the liver. The gall-bladder was distended with 

 gall of a light greenish colour — in the immediate change from 

 larva to adult it is of a dark colour. I had expected to find some 

 Trichodina in the thorax, but did not. The urino-seminiferous 

 organs, however, in both specimens of newt, were swarming with 

 animals in different stages of growth. This experiment goes to 

 prove that a long dearth of water has no effect on the existence of 

 the Trichodina as endoparasites. The other two I placed in their 

 natural element, and they soon recovered their activity. 



1 n reference to their vitality, I may remark that I tried in many 

 ways to keep them alive for anything approaching the time of the 

 control experiment, but all failed. At last, working on the assump- 

 tion that they required but little oxygen, the contractile vesicle 

 being anything but an active one, I constructed an oblong trough, 

 with the upper edges ground flat. In this I placed the viscera, 

 minus the lungs, liver, and heart ; at the same time syringing the 

 visceral cavity, and emptying the contents into the trough. This 

 I covered with a plate of glass, having previously greased the 

 edges, and placed the whole under the receiver of an air-pump. 

 By thus excluding a certain quantity of air, I was enabled to keep 

 most of them alive for about twenty-four hours. 



