ZOOLOGY. 351 



are to be considered centres of sensation or motion. In birds, it is 

 found that the greater area of sensitive surface in the legs corresponds to 

 the greater enlargement of the cord. Cuvier and Spalunzani observed 

 that bats are able to fly through intricate passages in the dark without 

 touching the walls, a faculty thought to be due to a minute net- work 

 of nerves distributed throughout the wing, arising from the superior 

 enlargement of the spinal cord. Thus it would seem that these portions 

 of the cord are intended to reinforce the function of sensation rather 

 than that of motion ; a view which agrees with the theories of recent 

 physiologists, that the spinal cord is a centre as well as a conductor of 

 nervous influence. Prof. Wi/man. Proc. Bos. Soc. Nat. His. 



*/ fc/ 



SEVENTEEN YEAH LOCUSTS. 



THE seventeen year locusts appeared in great numbers in various 

 parts of Maryland and Pennsylvania, during the months of May and 

 June, 18-51. The following description of the first appearance of the 

 insect above ground, and its transition to the winged state, is given by 

 Dr. Smith, of Baltimore : 



" AYhen they come up from the earth always about day-light or a 

 little before they immediately climb the first object they meet with, 

 a tree, a bush, or stake, anything two or three feet. They then lay 

 hold of the bark, fixing themselves firmly by their claws, and commence 

 working themselves out of their old shell, which is done by rupturing 

 it on the back, between the shoulders, and drawing themselves out. 

 As soon as they get fairly out, they seize hold of the old shell with their 

 claws, raise themselves, and begin to expand their wings. Their bodies 

 and wings at this time are exceedingly delicate, white and moist ; but 

 a few minutes' exposure to the air dries and hardens them, so that, by 

 the time the sun is fairly risen, they are perfect, and can fly. The 

 wings, before sloughing, are beautifully folded up, and it is a beautiful 

 sight to see them unfolded, and, in a few minutes, changed from the 

 most soft and delicate tissue to the firm and rigid wing of the perfect 

 insect. If it be a wet or very cloudy day they are apt to perish in the 

 operation of sloughing and drying." 



At the Boston Natural History Society, in June, Dr. Burnett fur- 

 nished an account of some observations recently made by him on the 

 structure of these locusts. He had found that, in the male, in many 

 instances, there is- scarcely a trace of a digestive canal, or biliary appa- 

 ratus, whereas, in the female, both are fully developed. This arrange- 

 ment is adapted to the peculiar wants of each ; the male living but a 

 few days, and the female much longer. The female, on emerging 

 from the earth, has about 500 eggs in her abdomen, of about one thir- 

 tieth of an inch in diameter, which is only about half their size at the 

 time they are deposited. The development of the eggs accounts for 

 the necessity of food and her complete digestive system. As the lo- 

 custs appear in about the same numbers at every period of their return, 

 it follows that only two of the eggs, on the average, are developed. It 

 would thus appear, supposing the production of these insects to have 

 always followed the same law, that there must have been originally a 



