EGG LAYING OF M. SUBNIGRESCENS 409 



APPLICATION TO THE oviJECTiON OF Mermis subnigrescens. 



The observations to date seem to shut out the possibility that ultra- 

 violet has much of anything to do with ovijection taking place natu- 

 rally in the open. The present observations seem again to make it 

 exceedingly probable that radiant heat must have much to do with it. 

 Recalling that the early morning light is relatively rich in red and 

 infra-red, and that as moisture (dew, rain) is essential, or at any rate 

 highly favorable, to the oviposition of M. subnigrescens, then obviously 

 early morning and forenoon would be a favorable time of day for the 

 oviposition. It is certain, from spectroscopic tests made during the 

 morning in question, that all the time after sunrise a good deal of blue 

 light was being passed through the atmosphere; and it therefore might 

 have been a behavior stimulus, and no doubt was so. 



All this harmonizes with previous experiments on the ovijection of 

 this species, an account of which is already published, and explains 

 the motive for the tests described above. 



Thus we have a fairly complete theory of the above-ground egg- 

 laying activities of Mermis subnigrescens. When the nema is ripe for 

 labor, she moves from her pitch dark, subterranean "domicile" to the 

 surface of the ground. Her movements during this trip no doubt 

 exemplify apogeo-, hydro-, thermo-, rheo-, thigmo-, and finally, just 

 before she reaches the surface, photo-tropism. 



Once her head is free of the surface of the ground, her chromatrope 

 comes into full play, "detecting" the direction and amount of light 

 from the sky, particularly, perhaps only, blue light. The structure of 

 the chromatrope is particularly adapted to the reception of light 

 from above or from any side, for the light will be concentrated in the 

 chromatrope by the transparent front tissues of the head acting as a 

 hemispherical lens, and the side tissues acting as a cylindrical lens. 



As she clambers higher and higher on the herbage, she responds to 

 such blue sky light as is not intercepted by the green blades of grass 

 and other foliage above and around her. Led by the blue light and 

 the urge to deposit, she will at last reach an elevation on the herbage 

 subject to a more direct action of the sun's rays, when the ovijector 

 and uterine muscles will be affected by "red" rays and ovijection will 

 begin; and this place in many instances would be at the altitude of 

 grazing grasshoppers, the definitive hosts. 



This would be a new and special parallel to the ordinary sequence of 

 events in ovijection and parturition. In other words the "voluntary" 

 nervous system comes first into play, bringing the organism into con- 



