5o6 POPULAR SCIENCE MONTHLY. 



than in the crawling forms; in the naked rather than in the armored; 

 in those of simple rather than in those of multiple organization — like 

 the arthropods; in those with lateral rather than in those with oral 

 limbs — ^like the mollusks; and finally in those with the smallest avail- 

 able number and most efficient character of limbs and other organs. 

 This leads us to the vertebrates for the highest type that appeared in 

 the waters of the earth, as the outcome of forms almost numberless 

 in variety. In this we have an oval-shaped elongated animal, its 

 organs of motion much the most effective of the many that had ap- 

 peared in the progress of life, its vital organs unified and simplified 

 to the greatest extent possible, its skeleton internal instead of external, 

 used solely as a support, in no sense as an armor. 



If we consider the fish in its most primitive varieties, we certainly 

 seem led to the conclusion that it is the form to which the evolution 

 of life would lead in any planet, as the basis of the higher develop- 

 ment. In Ampliioxus, for instance, we find the elongated bilateral 

 animal simplified to an extraordinary degree; without external armor 

 of any sort, with the simplest vital organs, with only the beginning 

 of an internal skeleton, and with merely the suspicion of a fin, virtu- 

 ally a flattening of the skin. In this form we have the vertebrate 

 reduced to its lowest terms, or the worm advanced to its highest. In 

 the hag we find again a boneless and scaleless creature, with a sheath 

 of cartilage to represent the backbone and with no organs of motion 

 other than a fin-like flattening around the tail. Much the same may 

 be said of the lamprey. From forms like these the fish seems to have 

 developed, with all its subsequent variations. 



The fish remains the highest form of water-developed life. It has 

 made comparatively slight steps of progress during the immense inter- 

 val since the paleozoic age. The limitations of its habitat seem to 

 have checked the development of organic form at this stage. It can 

 not be said that the evolution of life in the water has been in any sense 

 restricted by deficiency of time or narrowness of variation. The va- 

 riety of forms that have appeared is surprising when we consider the 

 uniformity of conditions in the water, and are only to be accounted 

 for as the result of a very active vital struggle. We find its simplest 

 and least specialized higher result in Amphioxus, of which the ultimate 

 result is the fish, beyond which, during millions of years, no progress has 

 been made. And a full consideration of what has taken place on the 

 earth strongly suggests that the oceanic evolution of life in any planet 

 must have ended at some not dissimilar stage. Mentally it stands at 

 a low level; and the whale, a mammal which has returned to the fish- 

 form, is as low as the fish in mental powers. 



Life in water was the basis of life on the land. It could not orig- 

 inate there de novo, land conditions being unadapted to the early life 



