160 



SCIENCE. 



[N. S. Vol. IV. No. 84. 



slept, or was inert, the otlier witli this dead 

 weight as a center could but describe a cir- 

 cle—a course which it found endless. Here 

 then arose a beautiful example of adapta- 

 bility. It learned to drag itself sideways, 

 wherever it would — over the whole yard. 

 This was the right half (never the left) 

 which has been spoken of as having a timid, 

 quick and irascible temperament. They 

 swam together well, but walked together 

 awkwardly. As they walked, the fore legs 

 acted simultaneously, so in turn the hind 

 legs, leaving alternately the front and back 

 of the shell without' support. Thus by a 

 slow teetering, or rocking gait, they could 

 go where they would. In starting they al- 

 most invariably pulled persistently in oppo- 

 site directions, which drew them laboriously 

 backward three or four feet. Eesting a 

 moment, they would start together, as 

 described above, and make the circuit of 

 the yard. 



With fate against them, they adapted 

 themselves to their condition so admirably, 

 and excited the admiration of so many that 

 a false and exaggerated value was put upon 

 them. Showmen offered sums out of all 

 proportion to the actual value, which were 

 rejected by the owners. 



If so highly prized then it should in all con- 

 sistency have been more zealously guarded. 

 But while at large with other similar pets, 

 a prowling cat singled out this one and 

 pounced upon it. It was secured at once, 

 but not before it had tumbled down the 

 stone steps leading to the cellar. 



It was returned to its aquarium, where 

 the right head came out from its protecting 

 shell at once ; likewise the left head a half 

 hour later. The next day it was itself again . 

 It ate, walked and swam as usual, save the 

 left head refused food, which was not un- 

 usual. The second day it was itself still, 

 though the left head would take no food. 

 On the third day it drooped. Though 

 rallying at times and hurrying about as 



usual, the left one was soon dead, as were 

 also the left legs. The cat's claw had 

 pierced the neck close to the shell. The 

 distress and uneasiness of the surviving 

 half was verj^ apparent. All its energies 

 and activities were redoubled, yet it died in 

 two and one-half hours later. Up to this 

 time its on\j sign of weakness was an occa- 

 sional gaping as if for more air. 



This little monstrosity's short life con- 

 tinued from the first of June to the middle 

 of September. 



Erwin Hinckley Barbour. 



The University of Nebraska. 



SOME DIFFICULTIES IN THE PRESENTATION 

 OF TEE PERIODIC LA W. 



The Periodic Law contains so much that 

 is true, and promises so much further reve- 

 lation as to the connection between the ele- 

 ments and the relations of their atomic 

 weights, valence and other properties, that 

 its permanent position in the science is as- 

 sured. It truly deserves the name of the 

 ]Sratural System, first given it by Mendeleeff, 

 but abandoned because it had been used 

 some twenty years before by Odling for a 

 verj^ different sort of arrangement. It stands 

 before us to-day as the statement of a nat- 

 ural law, though as yet undeveloped and im- 

 perfectly understood. There can, therefore, 

 be no question as to the acceptance of the 

 law of the inter- dependence of the atomic 

 weights and other properties, and the pecu- 

 liar relationship of the elements now known 

 as the Periodic Law. This must be the basis 

 of the science, and the proper formulation of 

 the law will contribute to a wonderful de- 

 velopment of it in the future. 



But there may well be question as to the 

 acceptance of any of the present statements 

 of the law. The systematic arrangements 

 of Mendeleeff or Meyer or Bayley are all 

 necessarily tentative because of the serious 

 imperfections in our knowledge. There is 

 a probability that new elements will be dis- 



