404 PHOTOTROPE 



affirmative answer was forecast, for the obvious reason, among others, 

 that, as the pigment must absorb certain light frequencies and transmit 

 others, the absorption might well result in some such changes of energy 

 as characterize vision. Very suggestive also is the fact that the trans- 

 parent, colorless parts of the head immediately in front of, and along- 

 side, the suspected phototrope condense light rays upon it. (See 

 Fig. 1.) 



Previous experiment showed the spectrum frequencies concerned in 

 bringing about ovijection in this nema probably to be some of those 

 in the light-blue and low violet region of the spectrum, together with 

 red (also infra-?). 3 It would therefore be natural to suspect, under 

 all the circumstances, that the cephalic pigment characteristic of the 

 adult female absorbs, and "makes use of," the frequencies present 

 just previous to and during ovijection. Hence a wish, (1), to deter- 

 mine what frequencies are present during and just previous to natural 

 ovijection; and, (2) to determine what frequencies are absorbed by the 

 cephalic pigment. 



In this field comparatively little seems to have been published, 

 though somewhat pertinent papers by Crozier, Mast, and others exist. 

 Investigators have been mainly occupied with the optics of the various 

 colorless, transparent, organic elements; the relative location and 

 probable function of certain pigments, usually dark or black (opaque) ; 

 and the "migration" and other changes of pigment, such as visual 

 purple, due to the action of light; and, of course, with the associated 

 nervous and contractile elements. Little has been published with 

 regard to tropism definitely due to the absorption of rays of a particular 

 frequency solely by transparent, colored pigment (other than visual 



but if possible better (to wit monosyllabic), terminology. The advantages of a mono- 

 syllable from which short, convenient adjectives, verbs, adverbs and other nouns can 

 readily be derived, are almost too obvious to need mention, tropic, tropically, to trope, 

 troping, etc., etc. Most helpful, perhaps, will be its use as a component, e. g., in 

 "chromatrope." 



Primarily "trope" denotes action, action that is in progress rather than completed. 

 By metonymy the word denoting an action (here, what is called a reaction) may be 

 applied to the (re)action-mechanism, i.e., in the present case, to the responding system 

 of intimately connected organs. 



Following this suggestion, we may speak of a reaction mechanism that aids or causes 

 an organism to face toward or away from light, as a phototrope; a reaction mechanism 

 used in orientation with reference to gravity, a geotrope, etc., etc., etc., etc.; thus the 

 statocystic mechanism of crustaceans is a species of geotrope. 



Accordingly, certain cephalic apparatus of Mermis subnigrescens is here spoken of as a 

 phototrope; or, better, because more specific, as a chromatrope, inasmuch as its reac- 

 tions apparently are to definite frequencies (colors) of the solar spectrum. Glaucotrope 

 y\avKO(7 = blue) may prove to be even more precise. 



3 Species of Mermis. Journ. Parasitology, 8 : 66. 1926. 



