PRELIMINARY NOTES ON THE ODONATA. 79 
added to the science of life, and, on the other, a group of beautiful 
insects has been systematized and placed beside the Lepidoptera and 
Coleoptera for purposes of more popular study. 
The Life Cycle. 
All aquatic organisms are especially interesting because they are 
nearer to the primitive and generalized products of evolution than are 
their more highly specialized terrestrial relatives. Not only did all 
life begin in the water but the seas were the early battle grounds of 
hosts of evolving races. For ages before the barren lands were clothed 
with vegetation, myriads of armored animals patroled the waters, rend- 
ing one another in continuous carnal warfare and laying the founda- 
tions for the changes to come. We read in the records of those times 
the chapters of phylogeny, but yet more, our science and philosophy 
seize upon forms which in the present day have risen only to the lower 
levels of organization, and make them contribute what they may possess 
to our perspective. And further, if to this lower stage of existence an 
animal adds a transformation to the terrestrial or aerial, and all in one 
life cycle shows us the primitive aquatic cell, the armored and pre- 
daceous Paleozoic monster and the best and swiftest aerial mechanism 
the world has ever known, our interest is more than doubled. This 
is true of the dragon-flies. 
The story of the development and transformation of the dragon- 
fly has been so frequently told that its treatment here will be brief. 
The cycle begins with the laying of the egg, either in the water or in 
some partly submerged stem, or even upon masses of floating plant 
debris. The eggs of different species vary in shape from elliptical to 
nearly spherical, and are usually a millimeter or less in length. Upon 
contact with the water the gelatinous covering becomes swollen by 
absorption and in some genera, as Tetragoneura, takes the form of a 
thread not unlike the egg strings of the toad. 
The egg hatches in a few days and there appears a curiously 
armored little nymph with large head and abdomen and a weak thorax 
bearing the six long, slender legs. The head is dorsi-ventrally com- 
pressed and accommodates a pair of rather large eyes, some short 
antennae and a remarkable labium. This latter is arm-like in struc- 
ture with its distal or lip portion supplied with a pair of strong man- 
dible-like appendages. When extended for grasping prey it reaches 
out several times the length of the head; when retracted the arm is 
folded beneath the head and thorax with the terminal portion arranged 
