NOTES AND MEMOBANDA. 171 



in from one to six hours, and the specimens were mounted in diluted 

 glycerine.* 



Spines of Echini. — The last published part of the ' Transactions 

 of the Eoyal Ii-ish Academy ' f contains a memoir by Mr. H. W. 

 Macintosh, B.A., on the structure of the spines in the sub-order 

 of the Desmosticha (Haeckel). In indicating four series into which, 

 judging from the structure of the spines, this sub-order may be 

 divided, the author expresses his opinion that the characters derived 

 from the spines are just as useful as any other characters di-awn from 

 the comparison of individual parts. He finds it just as easy and as 

 certain to recognize a Diadema, an Echinus, or an Arbacia by the 

 structure of its spines, as by the arrangement of its pores or the 

 disposition of its anal or genital plates. The paper is accom- 

 panied by three plates containing twenty-seven figures, all drawn 

 by the author with the assistance of a Wollaston's camera lucida. 

 The figures represent transverse sections of primary inter-ambulacral 

 spines of some twenty-six species, and have been drawn on stone by 

 Tuffen West with great care and accuracy .| 



The Locomotor System of Medusae. — Mr. G. J. Eomanes has con- 

 cluded his observations on this subject, which were commimicated to 

 the Eoyal Society in a paper read in January last.§ 



The principal bulk of the paper is devoted to a full consideration 

 of numerous facts and inferences relating to the phenomena of what 

 the author calls " artificial rhythm." Some of these facts have already 

 been published in abstract, || and to explain those which have not been 

 published would involve more space than it is here desirable to allow. 

 The tendency of the whole research on artificial rhythm, as produced 

 in various species of Medusfe, is to show that the natural rhythm of 

 these animals (and so probably of ganglio-muscular tissues in general) 

 is due, not exclusively to the intermittent natui'e of the ganglionic 

 discharge, but also in large measure to an alternate process of 

 exhaustion and restoration of excitability on the part of the respond- 

 ing tissues — the ganglionic period coinciding with that during which 

 the process of restoration lasts, and the ganglionic discharge being 

 thus always thrown in at the moment when the excitability of the 

 responding tissues is at its climax. 



Light has been found to stimulate the lithocysts of covered-eyed 

 Medusae into increased activity, thus proving that these organs, like 

 the marginal bodies of the naked-eyed Medusae, are rudimentary organs 

 of vision. 



The polypite of Aurelia aurita has been proved to execute move- 

 ments of localization of stimuli somewhat similar to those which the 

 author has already descriljed as being performed by the polypite of 

 Tiaropsis indicans. 



Alternating the direction of the constant current in the muscular 



* ' New York Medical Jour.,' Nov. 1878. 



t Vol. xxvi. (Science), Part 17. 



X ' Nature,' vol. xix. (1879) p. 319. 



§ 'Proc. Ko}'. Soc.,' vol. xxviii. (1879) p. 266. 



II ' Proc. Hoy. Soc.,' vol. xxv. p. 226. 



