EXTERNAL ANATOMY OF INSECTS. 409 



The only examples at present known are in some species 

 of Attelabus F. The head of these insects terminates 

 behind in a round tubercle, received in a corresponding 

 cavity of the thorax : the lower margin of this cavity has 

 a notch, and permits the movement of the head only in 

 one direction a ." 



2. The second kind of articulation, the ligamentous, 

 he affirms takes place only in orthopterous and some 

 neuropterous insects : " The head in this kind of articula- 

 tion is only impeded in its movements towards the back, 

 because it is stopped there by the advance of the pro- 

 thorax ; but below it is quite free. The membranes or 

 ligaments extend from the circuit of the occipital cavity 

 to that of the anterior part of the prothorax, which gives 

 a great extent to the movement b ." 



When I consider the well-deserved celebrity of the 

 great author whose words I have here quoted, and the 

 great and useful light that the genius and learning which 

 conducted his patient labours and researches have thrown 

 over every department of comparative anatomy, — a sci- 

 ence he may be almost said to have founded, — I feel the 

 most intire reluctance to differ in any thing from an au- 

 thority so justly venerable to all lovers of that interesting 

 study. But, however great my diffidence and hesitation 

 to express an opinion at all opposed to his, the interests 

 of truth and science require that I should state those 

 particulars in which my own observations, made upon a 

 careful examination of various insects of every Order, 

 have led to results in some respects different from the 



a Anat. Compar. i, 445—. b Ibid. 447. 



