480 NOTES 



a barrel organ, which plays with the greatest exactness a certain number of 

 tunes that are set upon it, but can do nothing else." .CARPENTER'S Mental 

 Physiology, p. 61. This constancy may be largely due to the uniformity 

 of conditions under which insects live. 



157 We may say, 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 honeycomb 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. 



158 An exception.to the general rule that the smaller animals have more 

 acute voices. 



159 It is wanting in a few, as the storks. 



160 The nightingale and crow have vocal organs similarly constructed, 

 yet one sings and the other croaks. 



lei Egg cells and sperm cells are detached portions of the parental or- 

 ganisms. Generally, 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 her- 

 maphrodite 



162 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 gepyornis, the great extinct bird' of Mada- 

 gascar, has the capacity of fifty thousand humming-birds' eggs. 



163 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, scratchers, and goatsuckers. 



164 This lies at first transversely to the long axis of the egg. As the 

 chick develops, it turns upon its side. 



165 The blood appears before the true blood vessels, in intercellular 

 spaces. It is at first colorless, or yellowish. 



166 Exactly as the blood in the capillaries of the lungs is aerated by the 

 external air. 



167 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 examples of arrested development. 



