Studies of Tissue Growth 



443 



apparent to the eye that a much wider band of new tissue had 

 grown from that half of the periphery which was cut deeper or 

 nearer the center (Fig./B). Measurements show that in two cases 

 the band of new tissue from the deep cut is twice as wide as that 

 from the shallow. The average of the eight other cases gives the 

 deep border one and one-half times the width of new tissue from 

 the shallow cut. 



Fig. 7 



Fig. 7 A, medusa disk with a semi-circular piece 20 mm. wide cut from one-half and a similar piece 

 10 mm. wide from the other. B, the stippled area indicates regeneration to proceed faster from the half 

 cut at the deeper level. 



The experiment demonstrates the influence of the level on the 

 rate of regeneration of tissue from two cut surfaces under nearly 

 identical physical conditions. I have shown ('07 and '08) that 

 when a bias-cut strip is removed from the entire periphery of a 

 medusa disk the new tissue regenerating from the strip and that 

 from the remaining disk center is proliferated at the same rate 

 from places on the two preparations which were originally adja- 

 cent. The rate of regeneration either towards the periphery or 

 towards the center is, therefore, the same from the same level. 



Ten individuals of Ophiocoma riisei had four of their five arms 

 removed. One arm was amputated at a point i cm. out from its 

 base of attachment to the disk, another 2 cm. from the disk, an- 

 other 4 cm. and a fourth 5 cm. out. On the same day ten indi- 

 viduals of Ophiocoma echinata were similarly operated upon. 

 These brittle-stars have one uninjured arm and the other four cut 



