Sept. 1897.] 
Dyar: Study of Young Arctians. 
131 
carya this process is foreshadowed on the metathorax, but while iia is 
partly united to i it forms a distinct wart on the mature larva. 
This parallelism between the relative advance of larval and imaginal 
characters is worthy of notice in view of the numerous cases of the re¬ 
verse tendency. 
The details of the seven selected species are shown in the accompany¬ 
ing plate. 
Spilosoma virginica. 
The setae aie perfectly normal for stage I, all the subprimaries 
absent. Of the six primary setae on the cervical shield, four remain on 
the shield, the others are detached and reduced, so that I detect only 
one seta on the small detached piece. The setae of the prespiracular 
tubercle are also less than in the primitive Tineid stock. On the other 
thoracic segments, ia and ib are united, iib separate and reduced, all 
characteristic of the Bombycine type of wart formation. On the abdo¬ 
men tubercle i is small, the rest large, vii with two setae on segments 1 
and 2, one on 7, 8 and 9, instead of the primitive three setae; leg 
plates well marked. Tubercle viii present next the midventral line (not 
shown in the figure). u Joint 13 ” is evidently composed of two seg¬ 
ments, on the anterior portion (9th abdominal) tubercles i to iii on one 
large wart, iv and v on another; on the anal plate (10th abdominal) all 
the five setae on a single disk. 
This is the type from which we start —an Arctian in the primitive 
first stage. 
Spilosoma antigone. 
The detached piece of the cervical shield is rudimentary. General 
tubercles as in virginica , except for a peculiar modification whereby 
tubercle iia on thorax has become three or four-haired (in different in¬ 
dividuals) and iii on abdominal segments 1 to 8, four or five-haired; 
on the ninth abdominal iii seems to be only three haired, as I find but 
five hairs on the large wart composed of tubercles i to iii. No subpri¬ 
mary setae; ventral setae as in virginica . 
This modification is to be interpreted as a partial wart formation, 
pushed back into stage I, yet unaccompanied by the subprimary setae, 
which in phylogeny must have preceded any wart formation. 
Not only in stage I is S. antigone unusually specialized for it genus, 
but in the later stages it has assumed the plumage and habits of Arctai 
(■ Eyprepia ), as noticed by Mr. Hulst (Ent. Amer., II, 16). This 
specialization is not shared by the imago, and is consequently without 
