1381.] 



Prof. J. A. Ewing. Effects of Stress. 



399 



violent agitation of the gills by the muscle attached to the stigmatic 

 pit would become useless, supposing an exposure of the gill-lamellse 

 to the atmosphere became by degrees habitual with the ancestral 

 Arachnidan. In proportion as these hypothetical creatures acquired 

 the habit of aerial respiration — the deepening and arching in of the 

 stigmatic pit would be favoured, and the atrophy and final disap- 

 pearance of the muscle which was attached to its inner surface, and 

 had mechanically brought it into existence, would also be directly pro- 

 moted. 



A further confirmation of the view now advanced is found in the 

 remarkable Javanese Arachnidan Thelyphonus. This Arachnid has 

 not four pairs of lung-sacs like Scorpio, but only two pairs, corre- 

 sponding to the two foremost lungs of Scorpio, and to the second 

 and third gill-book-pairs of Limulus. Nevertheless, the four segments 

 of the abdomen posterior to these are each marked by a pair of shallow 

 stigmata placed in line with the orifices of the pulmonary sacs of the 

 two anterior segments. When the internal structure corresponding to 

 these parts is examined, it is found that a large muscle (similar to the 

 similarly placed muscle of Limulus) is inserted into each of the four 

 right and four left stigmata in the segments posterior to the pul- 

 monary sacs. The two segments into which the two pairs of pulmo- 

 nary sacs are sunk, have no such muscles. The pulmonary sacs are, 

 therefore, in this case, also, to all appearance, enlarged muscular 

 stigmata, from which their former muscles have disappeared by 

 disuse and atrophy. 



XI. "Effects of Stress on the Thermoelectric Quality of Metals. 

 Part I." By J. A. EwiNG, B.Sc, F.R.S.E., Professor of 

 Mechanical Engineering in the University of Tokio, Japan. 

 Communicated by Professor Fleeming Jenein, F.R.S. Re- 

 ceived May 31, 1881. 



(Abstract.) 



This investigation was undertaken, in the first instance, with the 

 view of finding whether the gradual mechanical change which goes on 

 with lapse of time after stretching wires (which the author described 

 in a former paper, " Proc. Roy. Soc," vol. 30, p. 510) is associated 

 with a corresponding change in thermoelectric quality. But the expe- 

 riments brought to light some very unexpected results with regard to 

 the immediate effects of stress, and the present communication deals 

 with these only. Part I is further limited to the effects of longitudinal 

 pull on iron. The author is proceeding to extend the same inquiry to 

 other metals and to other modes of stress. 



