Packard.] INSECTS of the pond AND STREAM. 131 
is able to reflect on this progress of life as the beneficent 
result of the struggle, mental and physical, for existence, of 
his own and other species; such an one, unless his faculties 
are quite unequally developed, cannot avoid a rational com¬ 
bination of materialism and spiritualism in his intellectual 
make-up. The very faculty he possesses of making this 
retrospect and studying his own mental operations, and of 
appreciating the Infinite Power working in material laws, 
separates him from the animals, and should teach him that 
he is not subject alone to physical, material laws. 
So if, in looking back, the picture of the animal world 
evolving from a mere drop of protoplasm, of humanity 
struggling up from some ape-like 
form, seems sad, tragic, and gives a 
shock to the sensibilities of many, 
the final result is hopeful and inspir¬ 
ing. In connection with these pro¬ 
found problems of our own existence, 
the study of the habits, economy, 
structure and embryology of animals, 
their various contrivances for the 
maintenance of life, their evident en¬ 
joyment of life as long as it lasts, the 
gleams of intellect flashing out in their daily acts, all derive 
a fresh and startling interest. 
Among aquatic insects there are marvels of mechanical 
skill displayed in the construction of the bodies of the swim¬ 
ming and diving forms. The Gerris, or Wherryman (Fig. 
91), of our streams, ages ago anticipated our racing boats 
and wherries. Our diving machines, whether known to their 
inventors or not, are modelled on the principle of the diving 
beetle and the diving spider. The mechanism of swimming 
in the Dytiscus engaged the attention of Straus-Durchheim, 
the famous French anatomist. Models of scissors, straight 
and curved, that would give new ideas to a Sheffield manu- 
3 
Fig. 91. 
