Rev. T. Ilincks on the Pohjzoan Avicularium. 



23 



Fio-. 2. 



Fiff. .3. 



But in s]")ecimens from tlie Queen Charlotte Islands, which 

 have been placed in my hands by Dr. G. M. 

 Dawson, of the Canadian Geological Survey, the 

 appendage occurs in a very different guise : so far 

 as the mandibular portion is concerned, its appear- 

 ance is completely changed, and it is at gnce evi- 

 dent that a very important structural modification 

 has been effected. The mandible has altogether 

 lost its lid-like character, and is now a very tall S^ 

 membrano-chitinous appendage, commonly ex- 

 ceeding in length the entire cell, broad at the 

 base, and tapering off to a fine point above, where 

 it is slightly curved (woodcut, fig. 3). The expanded trian- 

 gular portion below, which represents the normal mandible, 

 has undergone little change ; but 

 its ofiice now is to support the 

 vibraculoid appendage which I have 

 described. Just above the point 

 wiiere the extremity of the true 

 mandible begins to expand into the 

 5'»r^<?^-vibraculum, there are two 

 small spinous projections ; these 

 mark the commencement of a mar- 

 ginal extension of the vibraculum, 

 whicli runs along each side from 

 this point to the apex, diminish- 

 ing in width as it approaches the 

 top. This marginal increment curls 

 upward, and gives a channelled 

 appearance to the appendage. The ■^" 



whole structure is of a membrana- ^^^t^- 



ceous character ; and there is always 



a slight twist near the base of it. When the transformed 

 mandible is at rest on the fixed beak, the free portion of it 

 occupies a suberect position. 



The modification is not confined in this case to the man- 

 dible, but extends to other elements of the structure. In the 

 first place, the rising on which the organ is placed is mucli 

 laro-er and more prominent than in the normal form, and 

 recalls the vibracular cell which supports the movable seta in 

 Mastiqophora Hjjndinanni. The beak also has undergone a 

 change which, though slight in itself, is significant. 



The anterior extremity, which in the normal condition is 

 directed straight outwards, running to a point, is liere more or 

 less notched, and we have a distinct suggestion of the vibra»- 

 cular cleft in which the seta of the more highly specialized 



