90 



SCIENCE 



[Vol. LV, No. 1413 



Many explanations of these declines and ex- 

 tinctions have been offered — a few absurd, 

 others plausible. Doubtless several causes 

 were involved in the result. But whatever the 

 cause may have been, it is evidently a law of 

 nature that the career of each type and of each 

 group must take the foim of a rising and 

 falling curve. 



"We now clearly understand that in the 

 course of this rise and fall of species, genera, 

 and larger groups, there has been a slow but 

 steady increase in complexity of structure and 

 in function, in both animal and plant bodies. 

 The worm has been succeeded by the more 

 highly constituted mollusk, which has in turn 

 been supplanted by the arthropod, the fish, 

 and finally the mammal. 



Each animal type seems to embody an ex- 

 periment to test the worth of one or more 

 important new devices which are the distinctive 

 contribution of that type to the progress of 

 animal develoiDment. 



The trilobites in the sea and the insects on 

 land introduced the wholly coordinated nervous 

 system and the power of rapid well-directed 

 motion, with better seeing powers and even 

 the possibility of fiight in the air. These 

 improvements represented a great advance 

 over the corals, which wait helplessly for their 

 food to drift into their mouths, or even over 

 such worms, starfishes and mollusks as slowly 

 grope through mud or sand or crawl with 

 proverbial snail's pace over the surface. In a 

 broad sense, the arthropods may be said to 

 have introduced into the world the rapacious 

 habit — the active pursuit of food. 



Another advance was represented by the 

 first vertebrates and particularly by the fishes, 

 which have attained nearest to perfection of 

 all water-inhabiting animals either previous or 

 subsequent. They invented the spindle form 

 and the stern propeller, both of which have 

 been imitated necessarily by every successful 

 swimming thing from the shark, the ichthyosaur 

 and the porpoise to the modern submarine 

 torpedo. The fishes also introduced the photo- 

 graphic or image-recording eye, which is far 

 superior to the light-sensitive spots of certain 

 echinoderms or even the remarkable compound 

 eyes of the insects. 



The reptiles in their turn devised the solid 

 bony skeleton without which active life upon 

 the dry land had previously been limited to 

 small animals such as the insects. They intro- 

 duced the encased egg, capable of being incu- 

 bated in air instead of water. This placed 

 the class one step ahead of the amphibians, 

 which must always remain near water. The 

 reptiles invented also a type of cover which 

 was able to withstand the evaporation of the 

 body liquids, without loss of that flexibility 

 which was essential for rapid motion. They 

 were not, however, so successful in coping 

 with that other element of climate — tempera- 

 ture. The chill of winter reduced their bodily 

 processes to inaction and obliged them to 

 hibernate except in the warmer months in the 

 year. For that reason they must always have 

 been, as they are now, largely confined to the 

 warmer parts of the globe. 



The probable descendants of the reptiles — 

 the mammals — somehow contrived that won- 

 derful invention, warm blood, and with it the 

 necessary heat-conserving cover of hair. These 

 enabled the mammals to range over nearly all 

 parts of the globe regardless of climatic and 

 seasonal changes and to maintain their bodily 

 activities constantly at the most favorable tem- 

 perature by oxidizing carbohydrates as bodily 

 fuel. It would be hard to overestimate the 

 importance of this innovation. 



(To be concluded) 



Eliot Blackweldee 

 Haevard University 



ON THE DIFFERENTIAL EFFECTS 



OF THE INFLUENZA EPIDEMIC 



AMONG NATIVE PEOPLES OF 



THE PACIFIC ISLANDS 



Since the influenza pandemic of 1917-1918, 

 the writer has had occasion to make two jour- 

 neys to insular areas of the Pacific Ocean, for 

 the prosecution of special field-studies. In 

 two specific instances, incidental observations 

 were mgde on the differential effects of the im- 

 ported disease upon the human inhabitants of 

 certain islands; it is the object of the present 

 brief communication to record the essential 

 facts. 



I. The first area is that of the Society 



