=o S 
ZOOLOGY. 367 
the same position in the two sexes of one species. It is some- 
- times less and sometimes more to the rear in the females than in 
the males and its situation depends on the relations existing 
between the different dimensions of the individuals. (5.) While 
standing, the centre of gravity is placed at the centre of the abdo- 
men, or in the posterior portion of the thorax, and usually in the 
centre of the length of the body. (6.) When an insect is walking 
its centre of gravity undergoes constant displacement about a 
mean point, but the distances of displacement are too small to be 
measured. (7.) The displacement of the centre of gravity when 
an insect passes from a state of repose to that of flight, cannot 
be ascertained except with those species where the wings lie 
folded on the back when in a state of repose. The displacement 
is horizontal, and from back to front. (8.) During active flight, 
the centre of gravity oscillates continually about a mean position 
which corresponds with the instants when the extremities of the 
Wings pass the point of crossing of the S-shaped curve which 
they describe in the air. (9.) In aquatic insects it is nearer to 
the lower than to the upper surface of the body. (10.) During 
Swimming, the movements of the posterior feet, acting like oars, 
determine the oscillation of the centre of gravity around a mean 
Position, which answers to the position of the swimming feet 
placed at the middle of their course.— A. W. B. 
Occurrence or rae SCISSOR-TAIL FLYCATCHER IN New JERSEY. 
On the 15th of April last, a magnificent specimen of the “ Scissor- 
tail” (Milvulus Jorficatus Swainson), was shot on the Crosswicks 
Meadows, five miles south of Trenton, N. J. The specimen was 
* male bird, in full health and feather ; weighing two and one-half 
| Sunces avoirdupois, and measuring thirteen and one-half inches 
_ itm the tip of the beak to the extremity of the tail. The bird, 
: men Captured, was busily engaged in picking semi-dormant 
 ‘MSects from the bark of the trees; creeping about very much as 
the custom of the Certhia Americana ; and all the while, opening 
q a shutting the long scissor-like tail. The stomach, on examina- 
_ Proved. to be full of small coleoptera, insects, eggs and flies. 
à — has been mounted, and will be forwarded to you in 
T ys. 
ie On reference to the Pacific R. R. Rep. vol. ix, page 168, we find 
Mat Prof, Baird states that the allied species, Milvulus tyrannus 
