ZOOLOGY. 45 
shape, and color. The question now arises, Do the Tra- 
cheata come from the Crustacea, or are they modified An- 
nelida? Plausible arguments have been advanced for the 
first of these views ; but the second, or that of the Tracheata 
coming from the Annelida, will be the one here adopted. 
On seeing for the first time the minute worm resembling 
an Annelid (Fig. 47), moving through the water, it would 
surprise the observer to learn that it was the larva, or unde- 
veloped young, of an Insect. The numerous segments of 
which the immature Insect and Spider are composed grad- 
ually coalesce, until finally the perfect Insect exhibits only 
three pieces, the Spider two. In the young ofthe Ephemera, 
or the one-day fly, and of the Libellula, small respiratory 
tufts are found externally, exactly as in the Annelida, which 
were alluded to in speaking of the brilliant colors of the 
Nereis. The existence in the larva of these external respi- 
ratory tufts, the manner of the development of the young 
of Insects and Spiders, furnishes the clue to their origin. 
The development, however, of the Myriapoda is just the 
reverse of that of the Insects, the Centipedes, etc. increasing 
instead of diminishing the number of their segments. Ori- 
ginally the body is composed of a congeries of cells, segment 
after segment being added, exactly in the same manner as 
in the case of the Annelida, with which in structure they 
closely agree, being adapted, however, to live on land. 
The Annelida seem then to be the ancestors of the Myria- 
poda, Insects, and Spiders, the Myriapoda retaining much 
of the Annelid structure through life, whereas the In- 
sect is an Annelid or Myriapod only when in a larval or 
undeveloped condition. That the development of the dif- 
ferent kinds of insects has been gradual, Geology seems 
to show, the evidences for which will be brought forward 
in the chapter on that subject. By looking at Tree 1V. the 
Hymenoptera will be seen very high up; this family includes 
the Bees, Ants, etc., whose economy has always been the 
