164 T. H. MORGAN. 



maxillarc. He cut the animal in two between the second and third 

 pairs of legs, and found in two cases that after a time a new part 

 suddenly appeared, presumably after a moult. This new part 

 that regenerated at the posterior end of the anterior piece Loeb 

 speaks of as a body, and points out that this is the first case 

 observed in the arthropods in which new body segments have 

 been seen to regenerate. I have repeated this experiment during 

 two summers, for it did not appear to me beyond dispute that the 

 new part that had been observed was necessarily a body, since no 

 satisfactory evidence that it was such is furnished -by Loeb's 

 paper. Although sections of the new part were, apparently, 

 made, no posterior opening of the digestive tract was found, no 

 ganglia are described as being present in the new body, nor do 

 new legs appear to have been present at the sides as we should 

 expect if this new part were really a body. 



My first experiments were made in 1901 and, although a 

 number of pycnogonids were kept for two months or longer, 

 none of them regenerated at the posterior end. Since I had used 

 large individuals it seemed not improbable that the lack of regen- 

 eration might have been connected with the maturity of the in- 

 dividuals. During the past summer I have repeated the experi- 

 ment on a large scale, both with large and with small individuals ; 

 but although many of the pieces were kept for nearly two months 

 no regeneration took place, with the possible exception of two 



instances that will be described. 



In a number of cases the individuals were cut in two between 



the third and fourth pairs of legs, i. e., nearer the posterior end 

 than Loeb had cut them, for, from analogy with other cases, it 

 seemed more probable that if the body could regenerate at all it 

 would be more likely to do so the nearer the cut was made to 

 the posterior end. Other individuals were cut in two between 

 the second and third pairs of legs. In only one case did regen- 

 eration appear to take place, as shown in Fig. I. Here the 

 bases of the fourth pairs of legs bulge out as though they had 

 been formed anew, and it seems possible that the rudimentary 

 abdomen is also new, although it is also possible that a part at 

 least of this structure had been left unintentionally when the cut 

 was made. Sections show that the digestive tract opens at the 



