No. 4-] PLAN ARIA MACULATA. 199 



in opposite directions when in a relaxed condition, but when 

 expanded form an angle of about 100. 



Morgan 1 has confirmed Spallanzani's discovery of earth- 

 worms regenerating a tail in place of a head. Sections of 

 these worms show a ventral cord extending to the new part, 

 that no brain is present, and that the nephrostomes in the 

 new part are turned backward towards the old part. 



Loeb, 2 in his investigations to determine the cause of animal 

 forms, produced monstrosities with hydroids in which the oral 

 end was regenerated on the aboral end. Loeb proposed the 

 term " heteromorphosis " for such monstrosities. Heteromor- 

 phosis not only includes the regeneration of a head in the 

 place of a tail, but of any organ in any place where in nature 

 one of unequal value would occur, as arms from the hips and 

 legs from the shoulders, etc. Loeb defines heteromorphosis 

 as " the replacement of one organ by another physiologically 

 and morphologically different." 



2. Analysis. -- The term " heteromorphosis " thus includes 

 the entire reversal of axial relations as well as the development 

 of any single organ in place of another. It will be useful to 

 distinguish these as polar heteromorphosis and heteromorpho- 

 sis of single organs. Examples of the latter are found in vari- 

 ous forms, as the regeneration of a tentacle-like organ in place 

 of an eye in crabs, etc. Examples of polar heteromorphosis, 

 on the other hand, with few exceptions, occur only among the 

 Coelenterates. 



Cerfontaine, 3 in his " Observations physiologiques sur 1'As- 

 troides calycularis," records the regeneration of a crown of 

 tentacles on the base of a severed part of a polyp. 



Loeb has found axial heteromorphosis to be quite common 

 among the coelenterates and has been able to produce it in 



1 "A Confirmation of Spallanzani's Discovery of an Earthworm Regenerating 

 a Tail in place of a Head," Abdruck aus dem Anatomischen Anzeigcr. Bd. xv, 

 pp. 407-410. 1899. 



2 Untersuchungen zur physiologischen Morphologic der Thiere. Bd. i, ii. \Yurz- 

 burg, 1891. 



3 " Notes preliminaires sur 1'organisation et le developpement de differentes 

 formes d'Anthrozoaides (deuxieme communication)," Bidl. de I'Acad. Roy. des 

 Sci., des Lettres et des Beaux-arts de Belgique. No. S, Notes v-viii. 1891. 



