344 THE POPULAR SCIENCE MONTHLY 



If phosphorescent organs produce a substance essentially a secre- 

 tion to which their characteristic activity is due, they might without 

 impropriety be classed as glands, but if they are thus classed, it must 

 be remembered that the majority of them are so placed that they have 

 no access to cavities or the exterior ; hence they would be in the nature 

 of ductless glands. In one respect, however, they differ even from 

 ductless glands; the substance that they produce is not carried away 

 from them even by the blood-stream but is used locally for the produc- 

 tion of light. Hence though phosphorescent organs may be in many 

 important respects like glands, they differ in certain ways from all 

 ordinary glands. 



Whether phosphorescent organs are under the control of nerves or 

 not is a question of some uncertainty. The fact that many highly 

 specialized phosphorescent organs have a rich innervation indicates that 

 they are under nervous influence, but even this may be of the indirect 

 kind such as has already been indicated for glands and not a direct 

 control. In ctenophores Peters (1905) has shown that a few paddle- 

 plates will glow on mechanical stimulation precisely as the rows of 

 plates in the normal animals do. He has also shown that the primitive 

 nervous system of these animals plays no direct part in this phos- 

 phorescence. This instance seems to me to be a perfectly clear case of 

 phosphorescence not under the control of nerves, though in an animal 

 with a nervous mechanism. 



In the common firefly the relations are not so well understood. 

 Thus Bongardt (1903), though he describes an intimate nervous plexus 

 in the luminous organ of this animal, believes that its rhythmic photo- 

 genic activity is not under even indirect nervous control. He main- 

 tains, on what, however, is not really strong experimental evidence, that 

 the firefly can not extinguish its light through nervous action and he 

 believes that the phosphorescent rhythm is due to totally different fac- 

 tors. This case merely shows the fragmentary nature of our knowledge 

 of this phenomenon even in so well-known an example as the firefly. 



As a good instance of nervous control over phosphorescence the 

 brittlestar, Ophiopsila, recently studied by Mangold (1907), may be 

 quoted. On mechanical stimulation the ventral surfaces of the arms 

 of this animal glow for a short time. The phosphorescence begins in 

 the stimulated part and, if this be an arm, it may spread over this arm 

 to the disk and thence to the other arms. The course that it follows is 

 that of the radial and circular nerve-strands. If any of these are in- 

 terrupted by being cut, the phosphorescence does not pass beyond the 

 cut, thus showing that it is probably controlled by the nerve. 



These instances, few and confessedly fragmentary as they are, indi- 

 cate that phosphorescent organs, though in many important respects 

 like glands, are in reality a separate class of effectors and that in some 



