200 



SCIENCE. 



[N. S. Vol. VII. No. 163. 



The duct runs straight forward along the 

 dorso-lateral margin of the plastron, then 

 back again, and, after many coilings, opens 

 into a large irregular chamber, or end- sac, 

 a remnant of the fifth coelomic cavity, situ- 

 ated in the middle of the posterior nephric 

 lobe. The embryonic nephric duct develops 

 as a tubular outgrowth of the ventral wall 

 of this cavity. Its distal end finally unites 

 with a short ectodermie ingrowth (readily 

 distinguished in the adult) , which opens at 

 the base of the fifth leg. 



The secretions from the four lobes of the 

 gland are collected by gradually widening 

 anastomosing tubules. Each lobe has many 

 separate openings into the large tubules of 

 the longitudinal stolon. The latter empty 

 into the coelomic space, or end-sac, and 

 from there a single nephric duct carries the 

 secretions to the external opening at the 

 base of the fifth leg. 



The glandular portion of the kidney de- 

 velops from six pairs of segmentally ar- 

 ranged 'anlagen.' Omitting all details, it 

 may be stated that a part of the fifth coe- 

 lomic cavity persists as the thin-walled 

 chamber, or end-sac, mentioned above. 



The other cavities of the thorax break 

 down after producing, by a thickening of 

 their neural walls, paired masses of finely 

 granular cells. These cells become hollow 

 and unite end to end to form irregular 

 groups of anastomosing tubules. The longi- 

 tudinal tubules of the stolon are formed in 

 a similar manner by the union of out- 

 growths from each cluster of cells. Many 

 tubes on the periphery of the gland retain 

 this unicellular condition in the adult, but 

 in the center of the lobes and in the longi- 

 tudinal stolon the nuclei of the tubules 

 have multiplied rapidly, giving rise to a 

 lining endothelium of flattened cells. 



The cell masses derived from the walls of 

 the first and sixth coelomic cavities disap- 

 pear. The remaining ones form the four 

 lobes of the adult kidney. 



The kidney of Limulus is, therefore, de- 

 rived from segmentally arranged groups of 

 excretory cells. Each group of cells prob- 

 ably emptied originally into its correspond- 

 ing coelomic cavity, and from there to the 

 exterior. These separate external openings 

 have now disappeared, and the organs are 

 united by longitudinal tubules which open 

 by a single duct, or coelomic funnel, to the 

 exterior. 



I consider the kidney, the nephric duct 

 and the genital duct of Limulus homologous,, 

 respectively, with the pronephros, the pro- 

 nephric duct and the Miillerian duct of Ver- 

 tebrates. 



Many of the details of the above account 

 were worked out in the biological laboratory 

 at Dartmouth by Miss Annah P. Hazen. 

 They will be fully described and illustrated 

 in a joint paper that we hope will appear at 

 an early date in the Journal of Morpliology. 



The Reaction of Amceba to Light of Different- 

 Colors and to Rontgen Rays. N. R. Har- 

 rington and Edward Leaming. 

 The physiological effect of Rontgen rays 

 upon undifferentiated protoplasm is almost 

 imperceptible as compared with the reaction, 

 produced by mechanical stimuli, heat, elec- 

 tricity or light. 



We have found that Amceba protens is ex- 

 tremely sensitive to changes in the color of 

 light in which it is placed, and that it ex- 

 hibits characteristic movements in different 

 light environments. 



The remarkably delicate condition of 

 phototonus is, we think, dependent 

 upon a favorable quality of light and an 

 optimum temperature. Continuance in a. 

 given color produces a more or less charac- 

 teristic flow ; in violet a spasmodic, unsuc- 

 cessful attempt to form pseudopods ; in 

 green or red a massive, diffuse bodily flow. 

 A quiescent Amceba brought from the 

 room light into red light begins to flow in 

 from, ten to twenty-five seconds. The flow 



