ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 319 



coagulating substance which induces in the ovum the elevation of the 

 vitelline membrane. 



New Devonian Ophiurid.* — F. A. Bather describes Sympterura minveri 



g. et sp. n., a Devonian Ophiurid from Cornwall. The genus is thus diag- 

 nosed : — A Lapworthurid with spinulosc disc extending to second arm- 

 segment, with oral skeleton of teeth, long jaws, and short mouth-frames 

 (torus not seen), with free arm-segments containing a vertebral ossicle, 

 possibly compound, grooved ventrally and provided on each side with 

 two wings, to the distal of which is attached an adambulacral spiniferous 

 element. The structure of the arm-segments suggests that the vertebrae 

 may be composed of two successive pairs of ambulacral elements, and 

 reasons are given for suspecting that this may be the case in all the more 

 advanced Ophiurids. The holotype of the species, which is the first 

 Echinoderm described from these Cornish slates, is in the British 

 Museum. 



Ccelentera. 



Movements and Reactions of Hydra.f — G-. Wagner has made a 

 careful study of the behaviour of Hydra viridis and other species. An 

 undisturbed Hydra contracts at fairly regular intervals ; after contraction 

 it expands in such a way as to occupy a different position from that 

 previously occupied. It has only one form of response to a single 

 mechanical stimulation, localised or non-localised ; this response is by 

 contraction, more or less complete, and not necessarily toward or away 

 from the stimulus. When a stimulus is repeated as soon as the polyp 

 has regained the expanded stage, contraction results as before. If a non- 

 localised mechanical stimulus is repeated at very brief intervals, say one 

 second, acclimatisation is soon effected, and the Hydra no longer 

 responds. A localised stimulus applied at such brief intervals brings, 

 about at first an apparent acclimatisation. This is soon followed in 

 many cases by the complicated " escape " movement, the Hydra moving 

 away from the region where stimulation occurs. This shows that the 

 physiological condition of the animal has been changed, so that to the 

 same stimulus under the same external conditions it now gives a reaction 

 different from that given at first. 



Hydra shows no orientation movements in response to stimulation by 

 a current of water. When the foot is detached the animal performs 

 active movements directed toward restoring the normal condition of 

 attachment. Geotaxis plays no part. Xon-locali$ed chemical stimuli 

 cause general contraction, except in certain food reactions. A strong 

 localised chemical stimulus causes a bending of the body or tentacles, as 

 the case may be, toward the side stimulated. The result is due to the 

 contraction of the ectoderm cells directly affected by the reagent, and is 

 non-adaptive. Hydra reacts to food only after a period of hunger. A 

 mechanical stimulus will not produce a discharge of nematocysts ; a 

 chemical stimulus does, probably by direct effect, in the area touched by 

 the reagent. The nematocysts can and do pierce the epidermis of the 

 prey, but Hydra seems able to paralyse prey without discharging 

 nematocysts. 



* Geo! Mng., ii. (1905) pp. 161-9 (1 pi.). 



t Quart. Journ. Micr. Sci., xlviii. (1905) pp. T85-G22 (0 figs.) 



