46 Papers jrom the Marine Biological Laboratory at Tortugas. 



The experiment clearly shows that, while the B group was regener- 

 ating the cut disk part in addition to the 5 oral-arms, the individuals 

 of B were decreasing in body size, as a result of this additional regenera- 

 tion, more rapidly than the specimens in A which were regenerating only 

 the 5 oral-arms. The regenerating tissue, through an excessive capacity 

 for the absorption of nutriment, draws upon the old body tissues and 

 causes them to decrease in size very much as one may suppose the rapidly 

 growing tumor to impose upon the substances of the surrounding body. 

 It is certainly clear that in both cases the growing tissue causes the old 

 body to become weak and emaciated while the growth itself continues 

 in a vigorous manner. 



The above experiment is of further value in regard to the influence 

 of the degree of injury on the rate of regeneration. I have previously 

 shown (loc. cit.} that the rate of oral-arm regeneration in this medusa 

 is independent of the degree of injury, as is also the case in the brittle- 

 star, Ophiocoma riisei, while O. echinata regenerates each arm the slower 

 the greater the number of removed arms. These results are contrary 

 to Zeleny's idea that the greater amount of injury will be followed by 

 a more rapid regeneration. 



The two groups of individuals A and B are each regenerating 5 oral- 

 arms, but the group B is the more extensively injured since a portion of 

 the disks was also cut away. If the additional injury or regeneration 

 imposed upon the B group exercises any influence on the rate of regenera- 

 tion, it should be shown by comparing the rates of growth of the arm-buds 

 in the two groups. The lower lines of table in give this comparison. 

 Those specimens with the disk uncut, or the least -injured ones, regener- 

 ated slightly more rapidly during the first 12 days, but after this time 

 the rates were practically equal. These facts show that an increased 

 injury to the medusa fails to give an increase in the subsequent regenera- 

 tion rates. 



A second experiment differed somewhat in manner of operation from 

 the one just described, yet the results are in perfect accord. Twenty- 

 eight healthy medusae were arranged in two groups of 14 individuals each 

 and operated upon as follows: The specimens of Group I had all of their 

 oral-arms and the central stomach mass entirely removed, leaving only 

 the medusa disk (fig. 3). Such a preparation lives and pulsates in a 

 normal manner and regenerates new tissue to cover over the central 

 stomach space. Then new oral-arms begin to bud from this tissue, until 

 finally the medusa regains its normal organs and parts. The central 

 space is first covered by a thin veil of tissue which tears repeatedly and 

 reforms until it begins to thicken, arid then the new arm -buds first 

 appear. The regenerative growth is therefore very vigorous from such 

 specimens during the early part of the experiment, and later becomes 

 much less. Group II was operated upon in the same manner as the 

 specimens of Group B in the above experiment, 5 oral-arms and a part 

 of the medusa disk were cut away (fig. 2). 



Tables iv and v contain the data from these specimens and table vi 

 facilitates a ready comparison of the averages. The original diameters 

 of each group averaged 88 mm.; after 14 days Group I was only 62 mm. 



