{11 ON ANIMAL LIFE 105 
familiar no such question intrudes. Among 
_ quadrupeds and birds, fishes and reptiles, 
there is no difficulty m deciding whether a 
given organism is an individual, or a part of 
an individual. Nor does the difficulty arise 
in the case of most insects. The Bee or But- 
terfly lays an egg which develops successively 
into a larva and pupa, finally producing Bee 
or Butterfly. Im these cases, therefore, the 
ego, larva, pupa, and perfect Insect, are re- 
garded as stages in the life of a single indi- 
vidual. In certain gnats, however, the larva 
itself produces young larvee, each of which 
develops into a gnat, so that the egg produces 
not one gnat but many gnats. 
The difficulty of determining what consti- 
tutes an individual becomes still greater among 
the Zoophytes. These beautiful creatures in 
many cases so closely resemble plants, that 
until our countryman Ellis proved them to be 
animals, Crabbe was justified in saying — 
Involved in seawrack here we find a race, 
Which Science, doubting, Knows not where to place ; 
On shell or stone is dropped the embryo seed, 
And quickly vegetates a vital breed. 
