448 



SCIENCE 



[N. S. Vol. XXVII. No. 690 



of behavior will be exhibited, depending 

 upon whether that zone comes to lie at a 

 proximal or a distal cut end. No stnac- 

 tural basis for this polarity has been 

 found. 



An Experimental Study of the Bate of Re- 

 generation in Cassiopea xa/machana: 

 Chas. R. Stockard, Cornell Medical 

 School. 



When a peripheral ring of tissue is re- 

 moved from the disc of Cassiopea the cut 

 surface promptly begins to regenerate a 

 new rim. The nearer the cut is made to 

 the center of the medusa-disc, up to a cer- 

 tain limit, the faster will the resulting re- 

 generation take place. 



Regeneration from variously shaped cut 

 surfaces proceeds in exactly the same man- 

 ner as has been described in experiments 

 on the fins of fishes. Thus the same prin,- 

 ciples of regeneration seem to apply to the 

 formation of new tissue from appendages 

 and the true body surface of animals. 

 Further, a common principle or law regu- 

 lating the rates of regeneration may prob- 

 ably run through the animal kingdom, since 

 forms at almost opposite ends of the series, 

 the fish and medusa, regenerate in a simi- 

 lar manner. 



A bias-cut strip of the entire periphery 

 of the medusa-disc and the remaining cen- 

 tral portion gives a preparation in which 

 the influences due to the level of the cut 

 may be contrasted with those due to de- 

 gree of injury. Influences due to the 

 level are alone indicated by the ensuing 

 growthi Regeneration in either direction, 

 towards the periphery or towards the disc- 

 center, proceeds at approximately the same 

 rate from the same level. 



Ring preparations made from these me- 

 dusse are splendid objects for the study of 

 the influences due to functional activity. 

 Portions of the ring which are entirely at 

 rest throughout the experiments regenerate 



tissue at the same rate as other parts which 

 pulsate normally. Functional activity 

 shows no influence over the rate of regen- 

 eration in this form. 



Medusffi having one or more of their 

 eight oral-arms removed regenerate these 

 arms at irregular rates which are not 

 closely associated with the degree of in- 

 jury. Medusffi injured to the same degree 

 often show greater variations in their 

 specific rates of regeneration than are 

 found among individuals injured to dif- 

 ferent degrees. A medusa with several of 

 its oral-arms cut away in a similar man- 

 ner may regenerate the individual arms at 

 rates differing as much as do the average 

 rates shown among many medusa injured 

 to various degrees. 



The influences of changed physical con- 

 ditions on the rate of regeneration were 

 tested, as well as the effects due to ex- 

 cesses of Na, K, Ca and Mg in the sea- 

 water. 



Regeneration of Peripheral Nerves: Ross 

 G. Haekison, Yale University. 

 The nerves of one side of the tail of 

 larvffi of Rana sylvatica, 2-2.5 cm. long, 

 were cut with fine scissors just beyond the 

 point of emergence from between the 

 myotomes. The processes of degenera- 

 tion and regeneration were then observed 

 from day to day in one and the same nerve 

 in the living specimen. The degenerative 

 processes take place very rapidly. In less 

 than twenty-four hours the medullary 

 sheath is completely disintegrated beyond 

 the lesion and for a very short distance 

 central to it. In the axis-cylinder of both 

 the meduUated and the non-meduUated 

 nerves the signs of degeneration are less 

 marked, though unmistakable, and are 

 noticeable in even the finest and most re- 

 mote twigs. The Schwann cells become 

 less regularly spindle shaped, with a some- 

 what humpy surface, and do not adhere 





