2oo Studies in the Theory of Descent. 



three species agree in marking to the extent of 

 their possessing in the adult form two rows of 

 ring-spots on each side, whilst the subdorsal line is 

 completely absent. 



The second group, consisting also of three 

 species, shows a great resemblance to Euphorbia > 

 but has only one row of ring-spots. It contains 

 D. Vespertilio, D. Galii, and the Algerian 

 D. Mauritanica. 



For the third group I only know one repre- 

 sentative, D. Livornica, Esp., which possesses a 

 single row of ring-spots connected by a subdorsal 

 line. 



Another group is composed of D. Zygophylli, 

 which occurs on the shores of the Caspian Sea, 

 and the North American D. Lineata ; these species 

 possessing a strongly-marked subdorsal line, asso- 

 ciated with more or less distinct ring-spots, which 

 I shall designate as " open rings," because their 

 black border does not intersect the subdorsal line, 

 but has the form of an arch above and below it. 



In the last group, represented by D. Hippophaes, 

 which occurs at the foot of the Alps (Wallis), and 

 southward as far as Andalusia, there is only a broad 

 subdorsal line, generally without any trace of a 

 row of spots. 



The important differences of marking displayed 

 by these five groups are not in any way accidental, 

 but they represent different stages of phyletic 

 development ; or, in other words, the five groups 



