1 66 T. H. MORGAN. 



opposite, and from this it seems probable that the original leg 

 had been lost at the breaking joint at the base, and a new one 

 had begun to regenerate. Moreover, I found one case in which 

 the new leg was clearly a new structure, Fig. 3. The different 

 segments had not yet been formed in their adult proportions and 



FIG. 3. 



the leg could not have been functional as yet. There is some 

 resemblance between this leg and the newly regenerated part 

 from the posterior end of the body that Loeb saw and figured. 

 In fact this idea seems to have suggested itself to Loeb for 

 he writes : " Das Vorhandensein eines ueberzahligen Segmentes 

 konnte vermuthen lassen, dass das neugebildete Stuck vielleicht 

 im Laufe der Zeit sich zu einer Extremitat entwickelt haben 

 wiirde, dass es sich also um die Bildung eines Beines an Stelle 

 des abgeschnittenen Rumpfstuckes gehandelt habe, ein Fall, den 

 ichals Heteromorphose bezeichnete. Allein Hoek fiihrt an, dass 

 bei Ammotheen das Abdomen nicht selten Spuren einer Segmenta- 

 tion zeigt." Thus in order to explain away the presence of too 

 many segments in the new part Loeb has recourse to a condition 

 found in another species a mode of explanation that will 

 scarcely recommend itself. 



A somewhat fuller analysis of these two cases of Loeb's may 

 not be unprofitable. If the new part is really a body, /. c., 

 thorax and abdomen, we should expect to find the digestive tract 

 opening at the posterior end, but this does not appear to have 

 been the case, for, Loeb says : " Der Darm setzte sich in clen 

 vorderen Theil des regenerirten Stiickes fort. Im Uebrigen aber 

 waren die Gewebe wenig differenzirt." It is to be remembered 

 that the digestive tract also continues out into the legs in the 

 pycnogonids as a blind sac. In the second place, while the three 

 segments of his first example might be interpreted as representing 

 the two remaining thoracic segments, and the rudimentary ab- 

 domen, yet in the other case five or six segments appear in the 

 new part. It is this that led Loeb to suggest that the new part 



