a 75 
tentacles in all directions. The Zrichodina 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; but 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 TZrichodina 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 Zrichodina at once attached themselyes to the Hydra. Both 
_ lived for days, the former seeming as much at home on the tentacles 
of the Hydra as on the branchiz of the larve of Zriton. 
8 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 TZrichodina 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 Zrichodina as endoparasites. The other two I placed in their 
_ natural element, and they soon recovered their activity. 
3 In 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. 
a _ In ny view the species of Zrichodina with which I have been 
