36 



Homofypical = homologous organs which 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 homodynamous. He arrives at the following definition 

 1. c, p. 15: „Two organs on different segments 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 difficult to tell 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 difficulties, 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 difficulties 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 Hepialus mustelinus). 

 These primary setae Fracker indicates by the characters of the 

 Greek alphabet, p. 28, because: 



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

 a limited group without disarranging the system. 



