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 (Tijdskr. 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. Scienc. 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 butterfly 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- 



