,04 



PSYCHK. 



THE DEVELOPMENT OF THE ROSTRUM IN RHYNCOPHOROUS 

 COLEOPTER A.— Plates VI-IX. , 



BY ETHEL M. MCCLENAHAN, LAKE FOREST, ILL. 



I. Introductory. 



Much has been learned of late from the study of the development of parts 

 which suddenly appear externally in insects at transformation. There remain a 

 few such parts which have not as yet received the attention of investigators. One 

 of these is the rostrum of rhyncophorous Coleoptera. Notwithstanding its size and 

 singular appearance, and the interest bestowed upon it as an adult structure by 

 systematists, I cannot discover that its development has received any attention 

 whatever. Although it is long, often longer than legs or wings, and although 

 appendage-like in appearance, it is not an appendage in the same sense as these, 

 but is a prolongation of the front part of the head and carries the antennae upon 

 its sides and the mouth parts at its tip. 



Dr. Le Conte, in the preface to his synopsis of the Rhyncophora of North Amer- 

 ica, in enumerating important questions for further study in the groups, said, "The 

 homologies of the parts of the head, by reason of which the front portion becomes 

 extended into a beak, and the basal piece on the under surface (which separates 

 the gular sutures in normal Coleoptera) disappears, are also worthy of attention." 

 This study of the development of the rostrum has been undertaken because it 

 seemed Hkely to yield answers to some of these questions of the systematist, and 

 at the same time to throw some new light on the general problems of meta- 

 morphosis. 



I have used, mainly, the two species of Rhyncophora, Mononychiis vulperulus 

 Fabr. and Ba/aniniis nasicus Say. The former lives its whole developmental life 

 in the capsules of the blue flag — a period of about nine weeks. ^ Balanimis nasi- 

 cus (Plate VI, fig. i) is known as the acorn weevil. The adult bores a hole into the 

 developing acorn and in it lays her egg. This takes place in the summer or early 

 fall. It soon hatches into a small white larva and grows rapidly, living upon the 



A detailed life history of this species has been given by Professor Needham. Biol. Bull. Vol. I, pp. 179-191. 



