390 



NOTES. 



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 moults at 

 least ten times before arriving at the winged state. 



118 Every tissue of the larva 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 matter. 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 enclosed 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. 



119 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. 



120 Excepting, perhaps, that the new tail of a Lizard is cartilaginous. 



121 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, in- 

 stead of the thumb. 



122 "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." — Mivart. 



123 It is, however, true that the number of eggs laid is proportioned to the 

 risk in development. 



124 According to Mr. Darwin, the characters which naturalists consider as 

 showing true affinity between two or more species are those which have been 

 inherited from a common parent ; and, in so far, all true classification is gene- 

 alogical; i. e., it is not a mere grouping of like with like, but it includes like 

 descent, the cause of similarity. In the existing state of science, a perfect 

 classification is impossible, for it involves a perfect knowledge of all animal 

 structure and life's history. As it is, it is only a provisional attempt to ex- 

 press the real order of nature, and it comes as near to it as our laws do in 

 explaining phenomena. It simply states what we now know about compar- 

 ative anatomy and physiology. As science grows, its language will become 

 more precise and its classification more natural. 



125 The term type is also used to signify that form which presents all the 

 characters of the group most completely. Each genus has its typical species, 

 each order its typical genus, etc. The word is also applied to the specimen 

 on which a new species is founded. A persistent type is one which has con- 

 tinued with very little change through a great range of time. The family of 

 Oysters has existed through many geological ages. 



126 The Ccelenterata and Echinodermata together make up the Radiata, 

 the old subkingdom of Cuvier. Echinoderma is probably more correct than 

 Echinodermata, but we retain the old orthography. 



