VI INTRODUCTION. 



kingdom. It has many side branches, it is true, but comparative anatomy, 

 embryology, and paleontology are in substantial agreement as to what kind of 

 animals and what organs and functions came first in time, what were the most 

 highly developed, and what was the general trend of evolution. 



Even the simplest vertebrates, that stand at the beginning of this long 

 series, were very highly organized animals, for all the fundamental systems of 

 organs well known to us in man, such as the sensory, nervous, skeletal, circulatory, 

 and excretory, were there fully established and highly efficient. But there is little in 

 the structure or development of these organs that gives us any positive information 

 as to their previous history, condition, or origin, the very information essential 

 to a true understanding of their meaning. 



On the other hand, when we look below the vertebrates for the main highway 

 of evolution, we are bewildered by the multiplicity of doubtful trails that appear 

 to have neither beginning nor end, that lead as readily in one direction as another. 

 Each invites us onward; but if followed, suspicion soon grows to conviction that 

 we have been deceived, that some other road is after all the right one. 



The familiar cry, "This way," "I have it," that rose when an enthusiastic 

 pioneer struck the annelid, tunicate, balanoglossus, or some other promising trail, 

 would for a time rouse great expectations; but it always ended in disappointment, 

 and gradually created an attitude of indifference, and the feeling that the solution 

 of this great problem was forever beyond our reach. The conviction grew that 

 one or more large classes of animals that once constituted the living trunk of 

 the genealogical tree during Silurian, or pre-Silurian times, were entirely extinct, 

 and had left no traces whatever behind. 



With the historic record of the most important period in the evolution of the 

 higher animals completely destroyed, the problem did indeed appear hopeless. 

 What was lacking in actual records was supplied by the speculative biologists, 

 and they did their work so well, and reiterated it so often, that it finally passed for 

 the truth, and its central idea, that the vertebrates had their origin in the 

 annelids, in some more or less roundabout way, became a dogma. 



We then witnessed the interesting phenomenon, common enough but always 

 profitable to contemplate, as lightning that strikes near by, that those who would 

 not make the annelid theory a part of their creed, and who continued the search 

 in other directions for a substantial body of facts to build upon, were branded 

 as morphological heretics and speculators, or as the victims of a too vivid imagina- 

 tion; and it was always the most "orthodox" and persistent speculator that 

 waved the hottest brand. 



But when the annelid dogma passed the period of productivity without off- 

 spring, even the orthodox biologists lost all hope of solving the real problem of the 

 origin of vertebrates, as well as many other large problems in invertebrate phy- 

 logeny, and turned their attention toward the Eldorado of cytology, heredity, 

 and experimental evolution, where "results" were easy and promised to carry far. 



Sterility has often turned devotion to contempt, and it is not suprising that the 



