among certain Annelules and Ophiurida. 109 



exist.* In the tinnelldes, again, in which each muscle is formed by a 

 single thread of muscular substance, which is often sufficiently irregular, 

 and in which, during the contraction, only a simple movement of retrac- 

 tion can be perceived, it was impossible to ascertain whether the move- 

 ment occurred in the whole muscle, or only in a part of it. But a con- 

 traction in the phosphorescent species being accompanied with light, 

 the verification of this fact became easy, and I believe I may safely con- 

 clude, from the facts above enumerated, that in the annelides, and also 

 the actiniidae and holothuriae just named, muscular contraction but 

 rarely takes place in the whole length of a muscle, or even of a single 

 fibre. Observations of this kind are made with more difficulty among 

 the ophiuridae, in which the muscular fibres are merged into each otiier, 

 and lost as it were in the general mesh work of the tissues ; but it is evi- 

 dent that analogy would authorize the admission of precisely' the same 

 conclusion in them, and even in those cases where we have the appear- 

 ance of isolated luminous points, as I have frequently witnessed, and 

 which at first does not appear confirmatory of the view. 



The annelides subjected to experiment have exhibited another fact 

 which appears equally worthy of attention. At the time I discovered 

 them in the fuci, which supplied them with a safe retreat, their move- 

 ments were prompt and energetic ; and the phosphorescence was equally 

 lively. Soon, however, they became languid, as regarded their loco- 

 motive powers, and the light became proportionably fainter. After a 

 time, it became necessary to excite them greatly, before a spark of any 

 brilliancy was obtained. At last they could not be roused at all, and 

 the light entirely disappeared. After leaving them, however, to repose 

 for a longer or shorter time, the}^ seemed to renew their strength, and 

 movement returned, together with the luminous phenomena. This kind 

 of lassitude, which was rather tardy in its manifestation in some of the 

 annelides, on the contrary exhibited itself verj^ promptly among the 

 ophiuridae. In these the phosphorescence was at first very conspicuous, 

 and their five arms were often illuminated from one extremity to an- 

 other ; but this brilliancy continued only for a few seconds, and the ani- 

 mal was quiet. Being stimulated, it again put itself in motion, but with 

 much less energy ; and the illumination disappeared equally rapidly. 

 Usually, I could obtain only seven or eight consecutive luminous dis- 

 charges : some of the most robust have afforded as many as nine. One 

 of these, after I had allowed it to rest for half an hour, gave, at the 

 end of this time, three other discharges, but they were far from being 

 strong. 



It thus appears very clearly, that the production of this luminosity 

 very much fatigues the animal, and rapidly exhausts it. Where any 



* See the Memoirs upon the Synaptes of Duvernoy, and on the Ed wards !a<!, 

 as well as the plates which accompany them, in the Annaks des Sciences Katu- 

 relles for IU'2. 



