296 



Hoiiiofi/piral = homologous organs whioh form the reflected images 



of' each other, hence antimers ; e. g. the right and 



left hands and the rays of a star-fish. 



Fracker therefore considers as homotypical what Claus-Grobben 



calls honiodynamous. He arrivés at the following definition 



1. c. p. 15: „Two organs on different segnients of the same animal 



are homotypic, regardless of their positions at the present time, 



when they have developed from homotypic organs of a generalized 



ancestor. In a generalized type two similar organs on different 



segments are homotypes, when they bear the same relations to 



the other organs of their respective segments". 



On the whole I agree with this definition, but I wish to point 

 out the hypothetic element which is hidden in it. It will often 

 be diflficult to teil how a certain seta is placed in a generalized 

 ancestral type, so that in most cases it will be better to trust 

 the second part of the definition rather than the first. Here we 

 meet with a great number of difïiculties, which Fracker places 

 under three headings: 



1. Absence of intermediate stages between radically different 

 conditions. 



2. The lack of developmental series. 



3. Apparently a lepidopterous larva has three or more entirely 

 distinct types of arrangement of the setae (prothoracic, thoracic, 

 abdominal, anal). 



Fracker obviates these difïiculties in the following manner, 

 1. c. p. 17: "The setae of the prothorax, metathorax and abdomen 

 of the generalized members of both sub-orders of Lepidoptera were 

 plotted, one segment over the other, as if all were on the same 

 segment. The number was about fifteen (fig. 1) and they were 

 in approximately the same position as on the prothorax of the 

 most generalized forms of the order." (in casu HepiaJü^ iinixfrlinNs). 

 These primary setae Fracker indicates by the cluiracters of the 

 Greek alphabet, p. 23, because: 



1. A special letter can be introduced for a subprimary seta in 

 a limited group without disarranging the system. 



