ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 759 



sight, and Prof. Preyer can only imagine that the just-named observers did 

 not sufficiently vary the conditions of their experiments. Thus, to follow a 

 straight line of escape is only one way among many. If a fresh Luidia be 

 electrically stimulated anywhere on its back, it may escape in curved, zig- 

 zag, or straight lines, and the latter do not by any means always lie between 

 the point of irritation and the centre of the mouth. The same holds good 

 for Asterias. Ophioderma, under the same conditions, makes quite irregular 

 attempts to escape. With Asterias a strong stimulus is sometimes followed 

 by no change of place, and Luidia often commits amputation. One of the 

 most remarkable phenomena offered by Asterids is their attempt to escape 

 from air. Thus, if two rays of an Asterias glacialis are placed in a narrow 

 tube filled with sea-water, while the other three rays remain in the air, the 

 latter will within ten minutes be drawn in, even though it were impossible, 

 without breaking the animal, to force it through. This is an indication of 

 the co-ordinated contractions of several thousands of muscles. After de- 

 scribing a large number of most interesting experiments. Prof. Preyer says 

 it would be useless to describe more showing with what judgment star-fishes 

 and brittle-stars free themselves from elastic rings, various coiled threads, nets, 

 and so on. The certainty and even the elegance with which they act cannot 

 but strike the observer, while again the number of superfluous twistings, 

 tactile movements, and locomotor actions diminish the more often the 

 creature is put to the test ; the variations in the angles formed by two rays 

 are quite astounding. The consensus of all the parts of a pentate or septate 

 nervous and muscular system is no less interesting from a physiological- 

 psychological point of view than the mechanism by which freedom is 

 gained. 



Dealing next with autotomy or self-amputation, the author commences 

 by remarking that the fact of many animals being able, under certain con- 

 ditions, to rid themselves of a part of their bodies is a physiological 

 problem of the first rank. He finds that autotomy must not be ascribed to 

 one cause only. Various observations dealing with this comparatively 

 well-known phenomenon are detailed, and it is pointed out that in Luidia, 

 at any rate, self-amputated pieces, when stimulated electrically, may break 

 up into two or even three pieces ; this shows, of course, that the central 

 nerve-ring is in no way necessary for autotomy. The observations all 

 together show that we have to do with a process of a special kind, and that 

 self-amputation is not always a reflex action. 



The succeeding chapter properly deals with the restoration of separated 

 parts ; after a reference to the well-known fact that pieces of star-fish with 

 which no portion of the disc remains connected may regenerate the four 

 other arms, it is pointed out that from a physiological point of view this 

 fact is especially noteworthy ; for Prof. Preyer has found that the central 

 nerve-pentagon of Echinoderms, or at least its five angles, from which the 

 radial medullse take their origin, are functionally (so far as co-ordinatiou 

 is concerned) more important than the radial medulla itself; yet in these 

 " comet " cases of reproduction the latter is alone sufficient to reproduce 

 the central organ. We have, within a year, a central nervous organ of a 

 high order formed completely afresh from a peripheral part of a lower 

 order. The fact that regeneration of Ophiurids cannot be effected without 

 the participation of the disc shows that, in them, the nerve-centre is 

 physiologically much more important than in Asterias. 



Although there is morphologically no essential difference in the value 

 of the rays, it was thought important to test the question from the physio- 

 logical side ; a number of experiments were performed, but no ray was 

 found to be of greater value than the rest ; some interesting facts were, 



