8 ON SOME INSECT DEFORMITIES. 
Mueller’s observation was accepted by the prominent naturalists of 
the time, —for instance, by Bonnet. Later J. F. Meckel (Handb. der 
pathol. Anatom., Vol. I, p. 55) explained the fact as an arrested devel- 
opment of the insect. Dr. Stannius (Mueller’s Archiv., 1835, p. 296) 
accepts this explanation. J. van der Hoeven (Tiydskr. voor natuurl. 
Gesch., Vol. VII, p. 274) believes the case to be just like that of Wes- 
mael and rejects the opinion of Mueller concerning the head; but I 
think he has not given strict attention to Mueller’s statements. 
Nymphalis Populi. 
Professor Wesmael gives in Bull. Acad. Bruxelles, 1838, Tom. IV, 
p- 359, reproduced partly in Ann. Science. Nat., Ser. 2, Vol. VIII, p. 191, 
a description and colored figure of this insect. If I am not mistaken, I 
saw, in 1870, the type in the Museum in Brussels. He caught the 
specimen in July, near this city. The insect had the thorax, abdomen, 
legs, and wings perfectly well developed and colored, but with the 
head of the caterpillar. The insect turned the curious head to the 
right and left, and. tried, by a quick motion of the forelegs, to push it 
off. Mr. Wesmael, in dissecting the left side of the head, discovered 
underneath the external skin a second one much thinner than the 
first, and beneath the second one the well-developed eye of the butter- 
fly. The parts around the eye were covered, as commonly, with scales. 
Therefore Wesmael considers the second skin as that of the chrysalis, 
and believes the deformity originated by the inability of the caterpillar 
to cast off the head. 
Underneath the head of the caterpillar, and just above the skin of 
the chrysalis, was the left antenna, coiled up, but without an apical 
knob. The antenna was covered by a very fine membrane, which was 
to a great extent diaphanous, and transversely striated with brown. 
The left palpus was free, normally developed, and turned horizontally 
backwards. The right palpus seemed broken off; the place of its in- 
sertion was clearly visible. Mr. Wesmael says nothing about the pro- 
thorax ; as the forelegs were free and movable, it must have been with- 
out any covering. 
This buttertly differs essentially from the moth described by Mueller. 
The head shows only the skin of the caterpillar, which really has gone 
through the transformation into the head of the chrysalis, and later 
into the head of the imago, retaining throughout the skin of the former 
stages, one above the other. The recorded movement of the head was 
apparently done by the movement of the head of the imago. Wesmael 
makes the following conclusions : — 
1. The insects which are obliged to undergo transformation may 
have only a partial one, which does not prevent the total transforma- 
