354 DR. N. ANNANDALE ON 



any other cause, buds which have recently been set free frequently survive them. 

 The same phenomenon occurs, so far as it is possible to judge, in the natural habitat ; 

 for at any rate the majority of individuals of the generations which succeed one 

 another in the " tanks ' ' during the year, originate as buds. 



Feeding. 



The feeding of European and North American species of Hydra has been dealt 

 with from different points of view by a large number of writers. I have little to add to 

 their observations, as the Bengal species does not differ at all notably from those of 

 colder latitudes in its methods of ingesting food. There are, however, one or two 

 observations on this function which I should like to record. In the first place, it has 

 been a matter of controversy as to what part the tentacles play, and whether they are 

 actually thrust into the mouth when food is swallowed. In the case of Hydra orien- 

 talis these organs are frequently introduced into the alimentary canal, and not only when 

 the animal is feeding. If a specimen is removed from any object to which it may be 

 adhering and placed in a watch glass full of water, a short period of complete retraction 

 both of the body and the tentacles takes place. Then the body becomes much elong- 

 ated and the tentacles moderately so. The mouth is often opened, and any food which 

 may be in the upper part of the alimentary canal is sometimes ejected. After this has 

 occurred the tips of the tentacles writhe in all directions and are repeatedly thrust 

 into the mouth and withdrawn again. During the process of ingestion the tentacles 

 are occasionally thrust into the mouth, but not invariably. 



As to the discharge of the nematocysts and their exact function, the largest form 

 of cell shoots out its stinging thread very much more readily than the smaller types do, 

 and this is the case whether the polyp is catching prey or merely suffers accident. Thus, 

 if a specimen is placed in a drop of water on a slide and a cover glass lowered gently 

 over it, a considerable number of the largest stinging cells explode and the thread is 

 emitted ; but if a drop of alcohol is allowed to mix with the water, a few of the smaller 

 threads are also shot forth. I have examined small Crustacea and Hydrachnids cap- 

 tured by the polyp and have always found the larger threads adhering to them, but 

 never the smaller. The discrepancies in the different accounts given of the discharge 

 of the nematocysts by different authors probably point to a variation as regards this 

 phenomenon both in respect to different species and to different conditions. 



In the latest account ' of the movements and reactions of Hydra it is stated that 

 the nematocysts are only discharged normally under the influence of chemical stimuli, 

 although they may be actually forced to emit their threads by direct pressure. On 

 the whole, such observations as I have made support this view ; the following espe- 

 cially. A small Hydrachnid came in contact with a tentacle of Hydra orientalis and 

 was captured by it. On an examination of the Hydrachnid I found that although the 

 polyp's nematocysts were scattered indiscriminately on the limbs of the prey and had 



1 By G. Wagner in Quart. Journ. Micr. Sci., Vol. XLVIII, 1905, p. 585. 



