410 EVIDENCE FOR CHROMATROPISM 



ditions favorable to the events about to follow. Thereafter the be- 

 havior is more or less "involuntary," as has been shown in the present 

 instance by the fact that ovijection continues under the stimulus of 

 sunlight, even if the head, including the chromatrope and central 

 nervous system, be removed, seared off. 



CIRCUMSTANTIAL EVIDENCE FOR THE CHROMATROPISM OF 



Mermis subnigrescens 



1. The commonly infested grasshoppers graze mostly within certain 

 limits above the ground; harmoniously, the eggs of the mermithid 

 parasite are found to occur preponderantly within these limits, sug- 

 gesting highly developed egg-laying instincts on the part of the nema 

 that might well presuppose tropism. 



2. A definite mechanism, believably a phototrope [includes chroma- 

 trope, (includes glaucotrope)] embodying what are believably recep- 

 tors, transmitters, and effectors, is present; a mechanism not other- 

 wise readily explicable. The only mermithid individuals known to 

 possess such a mechanism fully developed are those whose blackish 

 eggs are deposited in the way characteristic of Mermis subnigrescens. 



3. The putatively-chromatropic pigment absorbs, i.e., can be 

 sensitive to, blue rays. 



4. Only adult, chromatroped, egg-laying females clamber as de- 

 scribed. Males and young females having no power, or occasion, 

 to deposit eggs are not chromatroped. 



5. The clambering of the nemas ripe for oviposition is skyward; 

 i.e., toward blue sky, rather than vertical (distinction from negative 

 geotropism). Beams of blue light from the sky, often oblique, and 

 coming from many widely different directions, are those most certain 

 promiscuously to penetrate the depths of the herbage, and thus reach 

 to near the ground. The nema's lens-like tissues concentrating light 

 upon the chromatrope, accept it from above and from all sides; this 

 harmonizes with the distribution of blue sky light. 



6. Oviposition is stopped, or very much slowed, by green screens 

 (including living foliage) that absorb red and infra-red; indicating a 

 necessity for the nema to escape from exclusively green light before 

 oviposition can take place. In the grasshopper habitats, blue light 

 (sky-light) is the most diffused and most likely to be useful in leading 

 to the known consummation, should chromatropism come into play 

 at all. In nature, clambering skyward ('"blue-ward") from out the 

 green, brings the nema soonest under the incidence of the longer wave 

 lengths so stimulative to the ovijectors. 



