2 20 The Ohio Naturalist. [Vol. VIII, No. 2, 



when detached from the animal's body. Thus while a part of an 

 animal's organism may become regenerated, a new animal is 

 not produced in this process of regeneration. Even in those cases 

 where fragments of the animal's body give rise to new animals, 

 it is not always possible to obtain a new individual which would 

 be formed entirely of regenerated tissue, and which would in its 

 turn be ready to undergo an operation with subsequent regenera- 

 tion. 



Of all regenerating animals the fresh water oligochaet, Lum- 

 briculus, presents probably the best opportunity for such a 

 comparative study, since every piece of the worm, in fact any 

 single segment, be that from the anterior or posterior halves of 

 the worm's body, is capable of regenerating a new head as well 

 as a new tail. And furthermore, as I found, a regenerated tail 

 when severed from the old tissue may also regenerate a new head 

 and thus form a little worm, if kept under favorable conditions. 

 This little worm then is formed entirely of regenerated tissue, 

 but for all the rest so far as anatomical structure is concerned 

 it is identical with the parent organism. 



It is to the regeneration in these little worms, themselves 

 formed of regenerated tissue, that I directed my attention. 



Two pieces of approximately equal length, one from the an- 

 terior half and another from the posterior half of Lumbriculus 

 were left to regenerate for fourteen days. Let us name all these 

 pieces obtained from the front and hind portions of the worm, 

 A and B, respectively. I showed elsewhere that pieces taken 

 from the anterior region of worms regenerate at a higher rate than 

 those taken from more posterior regions. Thus, all the A pieces, 

 regenerated new tails with a rate of 4.4 segments on an average 

 to each one old segment; while the B pieces regenerated on the 

 average 2.6 segments per one old segment. To make this matter 

 clear I will illustrate it by an hypothetical case. Suppose that 

 all the A pieces and all the B pieces were composed of ten old 

 segments each, then the regenerated tails would on the average 

 have consisted of 44 and 26 new segments, I'espectively. 



At the end of fourteen days all the regenerated tails were cut 

 off. A large percentage of these detached regenerated tails re- 

 generated heads, and a new generation of worms, which presented 

 a race of dwarfed Lumbriculi, was thus originated. We will name 

 all these dwarfed worms a andb, the former being the descend- 

 ants of the A pieces, and the latter of the B pieces. 



After a while these little worms were also subjected to an 

 amputation of their tails, and were left to regenerate for a period 

 of fourteen days. At the end of this fortnightly period it was 

 found that tlie average number of regenerated segments per one 

 old segment was 0.1 1 in the a-worms, and 0.06 in the b-worms. 



Measuring the power of regeneration by the average number 



