464 RECORD OF CURRENT RESEARCHES RELATING TO 



of tlie tentacles of H. Boeselii is due to the influence of the formation 

 of colonies, just as the bilaterally symmetrical gi'ound-form of the 

 coral person is due to the same cause ; * the reason why this symme- 

 trical arrangement is not evident in the adult Hydra is that it separates 

 so soon from its parent stock, which is not the case with most corals ; 

 in fine, in H. Boeselii we only see the bilaterally symmetrical ground- 

 form in a nascent state. The typical number, of four, which, as 

 Haeckel has shown, is to be seen in the development of the Hydro- 

 medusae, and in the palseontological history of the Corals, has a reason 

 found for it in the fact that in the developing Hydra the number is 

 indefinite ; H. Boeselii has reached a stage in which two tentacles are 

 the first to apjjear, and then there appear two others at the points 

 where they are least confined ; this gives us the quadrate pyrami(J. 

 In many adult examples no more appear, and, where they do, the first 

 four can often be easily recognized. The reason why three do not 

 appear is that the first two develop under exactly similar conditions ; 

 if they were only succeeded by one tentacle a space would be left 

 which would be equally convenient for the development of another. 

 From these short notes it will be seen that although the paper is 

 almost unreadable on account of its profusion of technical terms, it is 

 exceedingly interesting as being an example of the strict application 

 of the so-called mechanical principles. 



Mode in which Hydra swallows its Prey-t — The current idea is 

 that Hydra swallows by taking its prey in its tentacles and turning 

 tentacles and all into its stomach. However, the part played by the 

 tentacles ceases as soon as the mouth comes in contact with the food. 

 The Hydra then slowly stretches itself over the food in a way that re- 

 calls to some extent the manner in which a serpent " gets outside " its 

 prey, or in which an automatic stocking might stretch itself on to 

 the foot and leg. No care seems to be taken, however, to present the 

 easiest point for deglutition, and an Entomostracon may be swallowed 

 sideways, for instance. So far are the tentacles from co-operating in 

 the act, that they are usually reflexed away from the food ; occasion- 

 ally, however, they are swung forward for a moment around the mass, 

 as if to ascertain how much remains to be swallowed. If the prey be 

 at all bulky, immediately after the whole act is completed the body- 

 cavity is everywhere filled and on the stretch, but after a short lai)se 

 of time the body contracts forcibly along the long axis, so that the 

 part containing the food is globular, supported on a slender foot, 

 and with a slender apical process bearing the tentacles around the 

 hypostome. 



Mr. M. M. Hartog thinks he has found a clue to the false idea 

 referred to. A Hydra that had swallowed a morsel larger than it- 

 self disgorged, as frequently observed, on his attemj^ting to take it up 

 for examination. On finding it half an hour after, three of its ten- 

 tacles were turned into its digestive cavity, whence they were succes- 

 sively and slowly withdrawn. As the mouth closes but slowly after 



* See this Joiu-nal, ii. (1879) p. 892. 



t ' Quart. Jourii. Micr. Sci.,' xx. (1880) p. 243. 



