EVENING DISCOURSES. 823 



Passing next to the movements of sea-anemones, coloured slides were exhi- 

 bited to show their general configuration, and in many their exquisite beauty 

 of coloration. The reflex actions, spontaneity, and co-ordination of movements 

 shown by these animals is by some attributed to the presence of a nervous system ; 

 others, such as Loeb, regard their movements and responses to stimulation as 

 due to the general characteristics common to all protoplasm. Loeb's experiments 

 of feeding a sea-anemone with a wad of paper dipped in crab juice, and another 

 wad moistened with sei water, were described, and also his experiments on 

 the beautiful Cerianthus. First the remarkable ' righting ' movements of a 

 Cerianthus placed head downwards in a glass tube, and then similar movements, 

 the animal righting itself when laid on a perforated zinc plate or wide-meshed 

 wire gauze — an example of what is called Geotropism. 



The remarkable observations of Bohn on Atlantic Actinia that live between 

 high and low water mark were referred to. The animals, when removed to an 

 aquarium where they are constantly and completely under water, expand their 

 tentacles at high water and close them at low water. This rhythm is retained 

 for several days. Parker's observations on Metridium were mentioned, as well as 

 those of Gamble and Keeble on Convoluta. 



The fascinating problems suggested by the rhythmically pulsating bells of the 

 Medusae or jelly-fish, so carefully investigated by Romanes, were next introduced. 

 Their forms and beauty were shown by coloured slides reproduced from the works 

 of Allman and Haeckel. The animal is propelled by the expulsion of water by 

 the contraction of its bell, so that the animal itself is propelled in the opposite 

 direction — a method adopted by some other aquatic animals. The contractions or 

 beats are as orderly as the beats of the human heart itself, and at once suggest a 

 comparison with cardiac rhythm. In the naked-eye Medusa (Sarsia), which was 

 shown, Romanes found that complete removal of the extreme margin of the bell 

 caused immediate total and permanent paralysis of the entire organ, while the 

 separated portion continues its contractions ; if a small piece of the margin is left 

 attached to the bell the umbrella still contracts. Romanes inferred that in the 

 naked-eye Medusas theie are centres of spontaneity for the origination of impulses 

 to which the contractions of the swimming-bell are exclusively due. The quiescent 

 marginless Sarsia, if stimulated mechanically, respond with a single beat, just 

 as does the ventricle of a frog's heart brought to a standstill by the application 

 of the first ligature of Stannius. The impulse to movement and co-ordination are 

 due, according to Romanes, to the presence of the nervous system, i.e. are 

 neurogenic, while Loeb from his experiments on Gonionemus — an American form 

 — ascribes the beat to ions which serve to bring about the labile equilibrium of 

 the colloid condition of the protoplasm. The locomotion of this simple animal is 

 due to the contraction and relaxation of one thin sheet of muscular fibres which 

 bring about co-ordination. During the contraction phase the bell does not respond 

 to stimulation; it is inexcitable or refractory — a stage called the 'refractory 

 phase.' It is this which prevents disharmony when multiple stimuli are applied 

 during the contractile phase. A refractory phase was first noticed in the heart 

 by Kronecker and Stirling many years ago. Marey studied it carefully and gave 

 it its present name. 



The Echinoderms represented by sea-urchins and starfish were next con- 

 sidered. The observations of Romanes and Preyer were illustrated by means of 

 slides. The movements of the tube feet were shown by the cinematograph ; then 

 followed a film to show their ' righting ' movements, and another to show 

 Astropecten burying itself in the sand by means of its tube feet. The researches 

 of Von Uexkull on these animals and on the brittle stars were next referred to and 

 similarly illustrated. Von Uexkull regards the sea-urchin as a ' republic of 

 reflexes.' The movements of a slug have to suffice for the Mollusca. The shadow 

 of a living slug was projected on a screen, and the retraction of its horns demon- 

 strated on the animal itself and the mechanism by which it is brought about by 

 means of a model. 



The subject of flight was dealt with very shortly, the observations of Da Vinci, 

 Pettigrew, Marey, Lendenfeld, and others being referred to, including the recent 

 researches of Mons. L. Bull carried out at the Marey Institut at Paris. By an 

 ingenious apparatus, a dragon-fly — Agrion — was cinematographed, and through the 

 kindness of M. Bull the original film was projected. The animal makes about 



