138 BRITISH LEPIDOPTERA. 



caudal horn to the 1st segment — (This also no longer forms the final stage of the onto- 

 geny of any species, but is retained in the 2nd stage of vespertilio, livomica, lineata). 



3. The subdorsal line bears a ring-spot on the penultimate segment ; the 

 other markings as in 2 — hippophaes. (A small number of specimens show a 

 transition to the following stage by the transference of ring-spots from the posterior 

 to the anterior segments.) 



4. Open ring-spots appear on the subdorsal line on all the segments from 

 the nth to the 1st — zygophylli, lineata. 



5. Closed ring-spots situated on the subdorsal line — livomica. 



6. A single row of ring-spots replaces the subdorsal line — gallii, vespertilio, 

 mauretanica. 



7. A double row of ring-spots — dahlii, euphorbiae, nicaea. (The two. 

 first-named reach this stage in the 4th stadium, nicaea in the 3rd.) 



He adds (loc. cit., pp. 199 et seq.), "The important differences 

 of marking displayed by these 5 sections are not in any way 

 accidental, but they represent different stages of phyletic develop- 

 ment, or, in other words, the five groups are of different ages, 

 the first (cipho7'biae, &c.) being the youngest, and the last 

 (hippophaes) the oldest of the group. According to their phyletic 

 age, the sections follow each other in inverse order, the first being 

 hippophaes, the second that of zygophylli, the third that of livomica, 

 the fourth that of gallii, the fifth and youngest that of euphorbiae." 

 Weismann, however, does not accept these as the natural sections 

 into which the Phryxids fall, e.g., he assumes lineal a to be a 

 generalised form of the more specialised livomica, whilst zygophylli 

 is a terminal species on the same phyletic plane as lineata, and 

 again he considers gallii and vespertilio as terminal forms, whilst 

 mauretanica, in the same plane, is considered merely a phyletic 

 stage in the development of dahlii, euphorbiae and nicaea (see loc. 

 cit., diagram, p. 358). His groupings, therefore, work out as : 



(1) hippophaes, (2) zygophylli, (3) lineata, livomica, (4) gallii, (5) 

 vespertilio, (6) mauretanica, dahlii, (7) euphoj'biae, nicaea. In 

 spite of the fragmentary knowledge we possess of the history 

 of the larvae of most of the Phryxid species, Weismann considers 

 (loc. cit., pp. 225 et seq.) that the development of the markings 

 has proceeded in the same manner in all the species. He points out 

 that (1) the species all appear to be making for the same goal, 



(2) the young larval forms of a species never show the markings 

 of a later phyletic stage than the older larval forms, (3) develop- 

 ment takes the same course in all species, only making a greater 

 advance in the same direction in some than in others, e.g., nicaea 

 and euphorbiae have advanced to the 7th phyletic stage, zygophylli 

 and hippophaes only to the 3rd, and some specimens of zygophylli 

 to the 4th, but, at whatever phyletic stage the ontogeny of a 

 species may terminate, the young larval instars always display the 

 older phyletic stages. Thus, gallii in its last ontogenetic instar 

 reaches the 6th phyletic stage, in its penultimate instar it reaches 

 the 5th phyletic stage, and in its 3rd instar the 4th phyletic stage 

 is represented, so that little imagination is required to anticipate 

 that, in the 2nd instar, the 3rd or 2nd phyletic stage would be 

 pictured. The ontogenetic instars may represent a continuous series 

 of phyletic steps, e.g., gallii, or certain steps may be omitted, e.g., 

 euphorbiae. The suppression of phyletic steps increases with the 

 advancement in phyletic development, the higher the step to which 

 the species finally attains, the greater is the tendency of the initial 



