NOTES. 377 
129 For this reason, Mammals are called viviparous ; but, strictly speaking, 
they are as oviparous as Birds. The process of reproduction is the same, 
whether the egg is hatched within the parent or without. The eggs of 
Birds contain whatever is wanted for the development of the embryo, ex- 
cept heat, which must come from without. Mammals, having no food- 
yolk, obtain their nutrition from the blood of the parent, and after birth 
from milk. Most of the sharks are viviparous. 
130 The larve of Butterflies and Moths are called caterpillars; those of 
Beetles, grubs ; those of Flies, maggots ; those of Mosquitoes, wigglers.—The 
terms larva, pupa, and imago are relative only; for, while the grub and cat- 
erpillar are quite different from the pupa, the bee-state is reached by a very 
gradual change of form, so that it is difficult to say where the pupa ends 
and the imago begins. In fact, a large number of Insects reach maturity 
through an indefinite number of slight changes. The Humble-bee molts at 
least ten times before arriving at the winged state. 
131 Every tissue of the caterpillar disappears before the development of 
the new tissues of the imago is commenced. The organs do not change 
from one into the other; but the new set is developed out of formless mat- 
ter.—The pupa of the Moth is protected by a silken cocoon, the spinning 
of which was the last act of the larva; that of the Butterfly is simply in- 
closed in the dried skin of the larva, which is called chrysalis because of its 
golden spots. The pupa of the Honey-bee is called nymph; it is kept in a 
wax-cell lined with silk, spun by the nursing-bee, not by the larva. The 
time required to pass from the egg to the imago varies greatly: the Bee 
consumes less than twenty days, while the Cicada requires seventeen years. 
132 Compare the amount of food required in proportion to the bulk of the 
body, and also with the amount of work done, in youth, manhood, and old 
age. 
183 Excepting, perhaps, that the new tail of a Lizard is cartilaginous. 
134 The patella, or knee-pan, has no representative in the fore-limb, and, 
strictly, it belongs to the muscular system rather than to the skeleton. 
Some anatomists contend that the great toe is homologous with the little 
finger, instead of the thumb. 
185 Tt is doubtful whether the dorsal tube of Insects and the heart of Mam- 
mals are homologous, as the circulatory organs of Invertebrates may prove 
to be homologous with the lymphatic system of Vertebrates. The jaw- 
bones and limb-bones of Vertebrates are homologous, according to some 
naturalists. 
86 Polarity begins, as we have already seen, in the very first change of 
an egg. 
87 The structure of the highest plants is more complex than is that of 
the lowest animals; but, for all that, powers are possessed by jelly-fishes 
of which oaks and cedars are devoid.—Mrvarr. 
88 Tt is, however, true that the number of eggs laid is proportioned to 
the risk in development. 
89 According to Mr. Darwin, the characters which naturalists consider as 
showing true affinity between any two or more species are those which 
have been inherited from a common parent, and, in so far, all true classifi- 
