NOTES. 
389 
103 ^y e ma y sa y > as a rule, that the proportion of instinct and intelligence 
in an animal corresponds to the relative development of the spinal cord and 
cerebrum. As a rule, also, the addition of the power to reason comes in 
with the addition of a cerebrum, and is proportioned to its development. 
Between the lowest Vertebrate and Man, therefore, we observe successive 
types of intelligence. Intelligence, however, is not according to the size of 
the brain (else Whales and Elephants would be wisest), but rather to the 
amount of gray matter in it. A honey-comb and an Oriole’s nest are con¬ 
structed with more care and art than the hut of the savage. It is true, this 
is no test of the capability of the animal in any other direction; but when 
they are fashioned to suit circumstances, there is proof of intelligence in one 
direction. 
104 An exception to the general rule that the smaller animals have more 
acute voices. 
105 It is wanting in a few, as the Storks. 
106 The Nightingale and Crow have vocal organs similarly constructed, yet 
one sings and the other croaks. 
i°7 These cells are detached portions of the parental organisms. Gener¬ 
ally, these two kinds of cells are produced by separate sexes; but in some 
cases, as the Snail, they originate in the same individual. Such an animal, 
in which the two sexes are combined, is called an hermaphrodite. 
108 The eggs of Mammals are of nearly uniform size; those of Birds, 
Insects, and most other animals are proportioned to the size and habits of 
the adult. Thus, the egg of the iEpyornis, the great extinct bird of Mada¬ 
gascar, has the capacity of fifty thousand Humming-birds’ eggs. 
109 As a general rule, when both sexes are of gay and conspicuous colors, 
the nest is such as to conceal the sitting Bird; while, whenever there is a 
striking contrast of colors, the male being gay and the female dull, the nest 
is open. Such as form no nest are many of the Waders, Swimmers, Scratch- 
ers, and Goatsuckers. 
110 This lies at first transversely to the long axis of the egg. As the chick 
develops, it turns upon its side. 
111 The blood appears before the true blood-vessels, in intercellular spaces. 
It is at first colorless, or yellowish. 
112 Exactly as the blood in the capillaries of the lungs is aerated by the 
external air. 
113 Thus, the hollow wing-bone was at first solid, then a marrow-bone, and 
finally a thin-walled pneumatic bone. The solid bones of Penguins are ex¬ 
amples of arrested development. 
114 The thigh-bone ossifies from five centres. The bone eventually unites 
to one piece. 
115 Muscle is mainly fibrine and myosin, while nerve is neurin. 
116 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, except 
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. 
117 The larvae of Butterflies and Moths are called caterpillars; those of 
